526 lines
20 KiB
Markdown
526 lines
20 KiB
Markdown
<!--[metadata]>
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+++
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title = "Docker container networking"
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description = "How do we connect docker containers within and across hosts ?"
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keywords = ["Examples, Usage, network, docker, documentation, user guide, multihost, cluster"]
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[menu.main]
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parent = "smn_networking"
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weight = -5
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+++
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<![end-metadata]-->
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# Understand Docker container networks
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To build web applications that act in concert but do so securely, use the Docker
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networks feature. Networks, by definition, provide complete isolation for
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containers. So, it is important to have control over the networks your
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applications run on. Docker container networks give you that control.
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This section provides an overview of the default networking behavior that Docker
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Engine delivers natively. It describes the type of networks created by default
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and how to create your own, user-defined networks. It also describes the
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resources required to create networks on a single host or across a cluster of
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hosts.
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## Default Networks
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When you install Docker, it creates three networks automatically. You can list
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these networks using the `docker network ls` command:
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```
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$ docker network ls
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NETWORK ID NAME DRIVER
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7fca4eb8c647 bridge bridge
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9f904ee27bf5 none null
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cf03ee007fb4 host host
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```
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Historically, these three networks are part of Docker's implementation. When
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you run a container you can use the `--net` flag to specify which network you
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want to run a container on. These three networks are still available to you.
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The `bridge` network represents the `docker0` network present in all Docker
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installations. Unless you specify otherwise with the `docker run
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--net=<NETWORK>` option, the Docker daemon connects containers to this network
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by default. You can see this bridge as part of a host's network stack by using
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the `ifconfig` command on the host.
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```
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$ ifconfig
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docker0 Link encap:Ethernet HWaddr 02:42:47:bc:3a:eb
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inet addr:172.17.0.1 Bcast:0.0.0.0 Mask:255.255.0.0
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inet6 addr: fe80::42:47ff:febc:3aeb/64 Scope:Link
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UP BROADCAST RUNNING MULTICAST MTU:9001 Metric:1
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RX packets:17 errors:0 dropped:0 overruns:0 frame:0
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TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
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collisions:0 txqueuelen:0
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RX bytes:1100 (1.1 KB) TX bytes:648 (648.0 B)
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```
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The `none` network adds a container to a container-specific network stack. That container lacks a network interface. Attaching to such a container and looking at its stack you see this:
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```
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$ docker attach nonenetcontainer
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root@0cb243cd1293:/# cat /etc/hosts
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127.0.0.1 localhost
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::1 localhost ip6-localhost ip6-loopback
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fe00::0 ip6-localnet
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ff00::0 ip6-mcastprefix
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ff02::1 ip6-allnodes
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ff02::2 ip6-allrouters
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root@0cb243cd1293:/# ifconfig
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lo Link encap:Local Loopback
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inet addr:127.0.0.1 Mask:255.0.0.0
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inet6 addr: ::1/128 Scope:Host
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UP LOOPBACK RUNNING MTU:65536 Metric:1
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RX packets:0 errors:0 dropped:0 overruns:0 frame:0
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TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
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collisions:0 txqueuelen:0
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RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
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root@0cb243cd1293:/#
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```
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>**Note**: You can detach from the container and leave it running with `CTRL-p CTRL-q`.
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The `host` network adds a container on the hosts network stack. You'll find the
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network configuration inside the container is identical to the host.
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With the exception of the `bridge` network, you really don't need to
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interact with these default networks. While you can list and inspect them, you
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cannot remove them. They are required by your Docker installation. However, you
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can add your own user-defined networks and these you can remove when you no
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longer need them. Before you learn more about creating your own networks, it is
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worth looking at the default `bridge` network a bit.
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### The default bridge network in detail
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The default `bridge` network is present on all Docker hosts. The `docker network inspect`
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command returns information about a network:
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```
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$ docker network inspect bridge
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[
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{
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"Name": "bridge",
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"Id": "f7ab26d71dbd6f557852c7156ae0574bbf62c42f539b50c8ebde0f728a253b6f",
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"Scope": "local",
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"Driver": "bridge",
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"IPAM": {
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"Driver": "default",
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"Config": [
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{
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"Subnet": "172.17.0.1/16",
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"Gateway": "172.17.0.1"
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}
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]
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},
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"Containers": {},
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"Options": {
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"com.docker.network.bridge.default_bridge": "true",
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"com.docker.network.bridge.enable_icc": "true",
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"com.docker.network.bridge.enable_ip_masquerade": "true",
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"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
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"com.docker.network.bridge.name": "docker0",
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"com.docker.network.driver.mtu": "9001"
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}
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}
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]
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```
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The Engine automatically creates a `Subnet` and `Gateway` to the network.
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The `docker run` command automatically adds new containers to this network.
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```
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$ docker run -itd --name=container1 busybox
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3386a527aa08b37ea9232cbcace2d2458d49f44bb05a6b775fba7ddd40d8f92c
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$ docker run -itd --name=container2 busybox
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94447ca479852d29aeddca75c28f7104df3c3196d7b6d83061879e339946805c
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```
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Inspecting the `bridge` network again after starting two containers shows both newly launched containers in the network. Their ids show up in the "Containers" section of `docker network inspect`:
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```
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$ docker network inspect bridge
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{[
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{
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"Name": "bridge",
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"Id": "f7ab26d71dbd6f557852c7156ae0574bbf62c42f539b50c8ebde0f728a253b6f",
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"Scope": "local",
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"Driver": "bridge",
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"IPAM": {
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"Driver": "default",
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"Config": [
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{
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"Subnet": "172.17.0.1/16",
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"Gateway": "172.17.0.1"
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}
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]
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},
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"Containers": {
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"3386a527aa08b37ea9232cbcace2d2458d49f44bb05a6b775fba7ddd40d8f92c": {
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"EndpointID": "647c12443e91faf0fd508b6edfe59c30b642abb60dfab890b4bdccee38750bc1",
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"MacAddress": "02:42:ac:11:00:02",
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"IPv4Address": "172.17.0.2/16",
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"IPv6Address": ""
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},
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"94447ca479852d29aeddca75c28f7104df3c3196d7b6d83061879e339946805c": {
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"EndpointID": "b047d090f446ac49747d3c37d63e4307be745876db7f0ceef7b311cbba615f48",
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"MacAddress": "02:42:ac:11:00:03",
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"IPv4Address": "172.17.0.3/16",
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"IPv6Address": ""
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}
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},
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"Options": {
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"com.docker.network.bridge.default_bridge": "true",
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"com.docker.network.bridge.enable_icc": "true",
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"com.docker.network.bridge.enable_ip_masquerade": "true",
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"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
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"com.docker.network.bridge.name": "docker0",
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"com.docker.network.driver.mtu": "9001"
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}
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}
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]
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```
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The `docker network inspect` command above shows all the connected containers and their network resources on a given network. Containers in this default network are able to communicate with each other using IP addresses. Docker does not support automatic service discovery on the default bridge network. If you want to communicate with container names in this default bridge network, you must connect the containers via the legacy `docker run --link` option.
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You can `attach` to a running `container` and investigate its configuration:
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```
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$ docker attach container1
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root@0cb243cd1293:/# ifconfig
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ifconfig
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eth0 Link encap:Ethernet HWaddr 02:42:AC:11:00:02
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inet addr:172.17.0.2 Bcast:0.0.0.0 Mask:255.255.0.0
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inet6 addr: fe80::42:acff:fe11:2/64 Scope:Link
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UP BROADCAST RUNNING MULTICAST MTU:9001 Metric:1
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RX packets:16 errors:0 dropped:0 overruns:0 frame:0
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TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
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collisions:0 txqueuelen:0
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RX bytes:1296 (1.2 KiB) TX bytes:648 (648.0 B)
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lo Link encap:Local Loopback
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inet addr:127.0.0.1 Mask:255.0.0.0
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inet6 addr: ::1/128 Scope:Host
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UP LOOPBACK RUNNING MTU:65536 Metric:1
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RX packets:0 errors:0 dropped:0 overruns:0 frame:0
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TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
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collisions:0 txqueuelen:0
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RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
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```
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Then use `ping` for about 3 seconds to test the connectivity of the containers on this `bridge` network.
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```
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root@0cb243cd1293:/# ping -w3 172.17.0.3
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PING 172.17.0.3 (172.17.0.3): 56 data bytes
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64 bytes from 172.17.0.3: seq=0 ttl=64 time=0.096 ms
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64 bytes from 172.17.0.3: seq=1 ttl=64 time=0.080 ms
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64 bytes from 172.17.0.3: seq=2 ttl=64 time=0.074 ms
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--- 172.17.0.3 ping statistics ---
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3 packets transmitted, 3 packets received, 0% packet loss
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round-trip min/avg/max = 0.074/0.083/0.096 ms
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```
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Finally, use the `cat` command to check the `container1` network configuration:
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```
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root@0cb243cd1293:/# cat /etc/hosts
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172.17.0.2 3386a527aa08
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127.0.0.1 localhost
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::1 localhost ip6-localhost ip6-loopback
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fe00::0 ip6-localnet
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ff00::0 ip6-mcastprefix
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ff02::1 ip6-allnodes
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ff02::2 ip6-allrouters
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```
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To detach from a `container1` and leave it running use `CTRL-p CTRL-q`.Then, attach to `container2` and repeat these three commands.
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```
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$ docker attach container2
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root@0cb243cd1293:/# ifconfig
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eth0 Link encap:Ethernet HWaddr 02:42:AC:11:00:03
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inet addr:172.17.0.3 Bcast:0.0.0.0 Mask:255.255.0.0
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inet6 addr: fe80::42:acff:fe11:3/64 Scope:Link
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UP BROADCAST RUNNING MULTICAST MTU:9001 Metric:1
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RX packets:15 errors:0 dropped:0 overruns:0 frame:0
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TX packets:13 errors:0 dropped:0 overruns:0 carrier:0
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collisions:0 txqueuelen:0
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RX bytes:1166 (1.1 KiB) TX bytes:1026 (1.0 KiB)
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lo Link encap:Local Loopback
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inet addr:127.0.0.1 Mask:255.0.0.0
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inet6 addr: ::1/128 Scope:Host
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UP LOOPBACK RUNNING MTU:65536 Metric:1
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RX packets:0 errors:0 dropped:0 overruns:0 frame:0
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TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
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collisions:0 txqueuelen:0
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RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
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root@0cb243cd1293:/# ping -w3 172.17.0.2
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PING 172.17.0.2 (172.17.0.2): 56 data bytes
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64 bytes from 172.17.0.2: seq=0 ttl=64 time=0.067 ms
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64 bytes from 172.17.0.2: seq=1 ttl=64 time=0.075 ms
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64 bytes from 172.17.0.2: seq=2 ttl=64 time=0.072 ms
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--- 172.17.0.2 ping statistics ---
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3 packets transmitted, 3 packets received, 0% packet loss
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round-trip min/avg/max = 0.067/0.071/0.075 ms
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/ # cat /etc/hosts
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172.17.0.3 94447ca47985
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127.0.0.1 localhost
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::1 localhost ip6-localhost ip6-loopback
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fe00::0 ip6-localnet
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ff00::0 ip6-mcastprefix
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ff02::1 ip6-allnodes
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ff02::2 ip6-allrouters
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```
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The default `docker0` bridge network supports the use of port mapping and `docker run --link` to allow communications between containers in the `docker0` network. These techniques are cumbersome to set up and prone to error. While they are still available to you as techniques, it is better to avoid them and define your own bridge networks instead.
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## User-defined networks
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You can create your own user-defined networks that better isolate containers.
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Docker provides some default **network drivers** for creating these
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networks. You can create a new **bridge network** or **overlay network**. You
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can also create a **network plugin** or **remote network** written to your own
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specifications.
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You can create multiple networks. You can add containers to more than one
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network. Containers can only communicate within networks but not across
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networks. A container attached to two networks can communicate with member
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containers in either network. When a container is connected to multiple
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networks, its external connectivity is provided via the first non-internal
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network, in lexical order.
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The next few sections describe each of Docker's built-in network drivers in
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greater detail.
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### A bridge network
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The easiest user-defined network to create is a `bridge` network. This network
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is similar to the historical, default `docker0` network. There are some added
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features and some old features that aren't available.
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```
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$ docker network create --driver bridge isolated_nw
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1196a4c5af43a21ae38ef34515b6af19236a3fc48122cf585e3f3054d509679b
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$ docker network inspect isolated_nw
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[
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{
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"Name": "isolated_nw",
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"Id": "1196a4c5af43a21ae38ef34515b6af19236a3fc48122cf585e3f3054d509679b",
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"Scope": "local",
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"Driver": "bridge",
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"IPAM": {
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"Driver": "default",
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"Config": [
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{
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"Subnet": "172.21.0.0/16",
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"Gateway": "172.21.0.1/16"
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}
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]
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},
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"Containers": {},
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"Options": {}
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}
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]
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$ docker network ls
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NETWORK ID NAME DRIVER
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9f904ee27bf5 none null
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cf03ee007fb4 host host
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7fca4eb8c647 bridge bridge
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c5ee82f76de3 isolated_nw bridge
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```
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After you create the network, you can launch containers on it using the `docker run --net=<NETWORK>` option.
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```
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$ docker run --net=isolated_nw -itd --name=container3 busybox
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8c1a0a5be480921d669a073393ade66a3fc49933f08bcc5515b37b8144f6d47c
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$ docker network inspect isolated_nw
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[
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{
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"Name": "isolated_nw",
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"Id": "1196a4c5af43a21ae38ef34515b6af19236a3fc48122cf585e3f3054d509679b",
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"Scope": "local",
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"Driver": "bridge",
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"IPAM": {
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"Driver": "default",
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"Config": [
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{}
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]
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},
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"Containers": {
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"8c1a0a5be480921d669a073393ade66a3fc49933f08bcc5515b37b8144f6d47c": {
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"EndpointID": "93b2db4a9b9a997beb912d28bcfc117f7b0eb924ff91d48cfa251d473e6a9b08",
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"MacAddress": "02:42:ac:15:00:02",
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"IPv4Address": "172.21.0.2/16",
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"IPv6Address": ""
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}
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},
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"Options": {}
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}
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]
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```
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The containers you launch into this network must reside on the same Docker host.
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Each container in the network can immediately communicate with other containers
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in the network. Though, the network itself isolates the containers from external
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networks.
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Within a user-defined bridge network, linking is not supported. You can
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expose and publish container ports on containers in this network. This is useful
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if you want to make a portion of the `bridge` network available to an outside
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network.
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A bridge network is useful in cases where you want to run a relatively small
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network on a single host. You can, however, create significantly larger networks
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by creating an `overlay` network.
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### An overlay network
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Docker's `overlay` network driver supports multi-host networking natively
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out-of-the-box. This support is accomplished with the help of `libnetwork`, a
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built-in VXLAN-based overlay network driver, and Docker's `libkv` library.
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The `overlay` network requires a valid key-value store service. Currently,
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Docker's `libkv` supports Consul, Etcd, and ZooKeeper (Distributed store). Before
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creating a network you must install and configure your chosen key-value store
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service. The Docker hosts that you intend to network and the service must be
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able to communicate.
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Each host in the network must run a Docker Engine instance. The easiest way to
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provision the hosts are with Docker Machine.
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You should open the following ports between each of your hosts.
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| Protocol | Port | Description |
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|----------|------|-----------------------|
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| udp | 4789 | Data plane (VXLAN) |
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| tcp/udp | 7946 | Control plane |
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Your key-value store service may require additional ports.
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Check your vendor's documentation and open any required ports.
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Once you have several machines provisioned, you can use Docker Swarm to quickly
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form them into a swarm which includes a discovery service as well.
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To create an overlay network, you configure options on the `daemon` on each
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Docker Engine for use with `overlay` network. There are three options to set:
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<table>
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<thead>
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<tr>
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<th>Option</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><pre>--cluster-store=PROVIDER://URL</pre></td>
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<td>Describes the location of the KV service.</td>
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</tr>
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<tr>
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<td><pre>--cluster-advertise=HOST_IP|HOST_IFACE:PORT</pre></td>
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<td>The IP address or interface of the HOST used for clustering.</td>
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</tr>
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<tr>
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<td><pre>--cluster-store-opt=KEY-VALUE OPTIONS</pre></td>
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<td>Options such as TLS certificate or tuning discovery Timers</td>
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</tr>
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</tbody>
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</table>
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Create an `overlay` network on one of the machines in the Swarm.
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$ docker network create --driver overlay my-multi-host-network
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This results in a single network spanning multiple hosts. An `overlay` network
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provides complete isolation for the containers.
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|
Then, on each host, launch containers making sure to specify the network name.
|
|
|
|
$ docker run -itd --net=my-multi-host-network busybox
|
|
|
|
Once connected, each container has access to all the containers in the network
|
|
regardless of which Docker host the container was launched on.
|
|
|
|
|
|
|
|
If you would like to try this for yourself, see the [Getting started for
|
|
overlay](get-started-overlay.md).
|
|
|
|
### Custom network plugin
|
|
|
|
If you like, you can write your own network driver plugin. A network
|
|
driver plugin makes use of Docker's plugin infrastructure. In this
|
|
infrastructure, a plugin is a process running on the same Docker host as the
|
|
Docker `daemon`.
|
|
|
|
Network plugins follow the same restrictions and installation rules as other
|
|
plugins. All plugins make use of the plugin API. They have a lifecycle that
|
|
encompasses installation, starting, stopping and activation.
|
|
|
|
Once you have created and installed a custom network driver, you use it like the
|
|
built-in network drivers. For example:
|
|
|
|
$ docker network create --driver weave mynet
|
|
|
|
You can inspect it, add containers to and from it, and so forth. Of course,
|
|
different plugins may make use of different technologies or frameworks. Custom
|
|
networks can include features not present in Docker's default networks. For more
|
|
information on writing plugins, see [Extending Docker](../../extend/index.md) and
|
|
[Writing a network driver plugin](../../extend/plugins_network.md).
|
|
|
|
### Docker embedded DNS server
|
|
|
|
Docker daemon runs an embedded DNS server to provide automatic service discovery
|
|
for containers connected to user defined networks. Name resolution requests from
|
|
the containers are handled first by the embedded DNS server. If the embedded DNS
|
|
server is unable to resolve the request it will be forwarded to any external DNS
|
|
servers configured for the container. To facilitate this when the container is
|
|
created, only the embedded DNS server reachable at `127.0.0.11` will be listed
|
|
in the container's `resolv.conf` file. More information on embedded DNS server on
|
|
user-defined networks can be found in the [embedded DNS server in user-defined networks]
|
|
(configure-dns.md)
|
|
|
|
## Links
|
|
|
|
Before the Docker network feature, you could use the Docker link feature to
|
|
allow containers to discover each other. With the introduction of Docker networks,
|
|
containers can be discovered by its name automatically. But you can still create
|
|
links but they behave differently when used in the default `docker0` bridge network
|
|
compared to user-defined networks. For more information, please refer to
|
|
[Legacy Links](default_network/dockerlinks.md) for link feature in default `bridge` network
|
|
and the [linking containers in user-defined networks](work-with-networks.md#linking-containers-in-user-defined-networks) for links
|
|
functionality in user-defined networks.
|
|
|
|
## Related information
|
|
|
|
- [Work with network commands](work-with-networks.md)
|
|
- [Get started with multi-host networking](get-started-overlay.md)
|
|
- [Managing Data in Containers](../containers/dockervolumes.md)
|
|
- [Docker Machine overview](https://docs.docker.com/machine)
|
|
- [Docker Swarm overview](https://docs.docker.com/swarm)
|
|
- [Investigate the LibNetwork project](https://github.com/docker/libnetwork)
|