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Network scoped alias support

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Signed-off-by: Madhu Venugopal <madhu@docker.com>
This commit is contained in:
Madhu Venugopal 2016-01-08 05:45:56 -08:00
parent 349d9700bd
commit dda513ef65
14 changed files with 238 additions and 2 deletions
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124
docs/userguide/networking/work-with-networks.md
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@ -499,6 +499,130 @@ environment variables into a running container without significant effort and he
it is not compatible with `docker network` which provides a dynamic way to connect/
disconnect containers to/from a network.
### Network-scoped alias
While `links` provide private name resolution that is localized within a container,
the network-scoped alias provides a way for a container to be discovered by an
alternate name by any other container within the scope of a particular network.
Unlike the `link` alias, which is defined by the consumer of a service, the
network-scoped alias is defined by the container that is offering the service
to the network.
Continuing with the above example, create another container in `isolated_nw` with a
network alias.
```bash
$ docker run --net=isolated_nw -itd --name=container6 --net-alias app busybox
8ebe6767c1e0361f27433090060b33200aac054a68476c3be87ef4005eb1df17
```
```bash
$ docker attach container4
/ # ping -w 4 app
PING app (172.25.0.6): 56 data bytes
64 bytes from 172.25.0.6: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.6: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=3 ttl=64 time=0.097 ms
--- app ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
/ # ping -w 4 container6
PING container5 (172.25.0.6): 56 data bytes
64 bytes from 172.25.0.6: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.6: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=3 ttl=64 time=0.097 ms
--- container6 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
```
Now let us connect `container6` to the `local_alias` network with a different network-scoped
alias.
```
$ docker network connect --alias scoped-app local_alias container6
```
`container6` in this example now is aliased as `app` in network `isolated_nw` and
as `scoped-app` in network `local_alias`.
Let's try to reach these aliases from `container4` (which is connected to both these networks)
and `container5` (which is connected only to `isolated_nw`).
```bash
$ docker attach container4
/ # ping -w 4 scoped-app
PING foo (172.26.0.5): 56 data bytes
64 bytes from 172.26.0.5: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.26.0.5: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.26.0.5: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.26.0.5: seq=3 ttl=64 time=0.097 ms
--- foo ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
$ docker attach container5
/ # ping -w 4 scoped-app
ping: bad address 'scoped-app'
```
As you can see, the alias is scoped to the network it is defined on and hence only
those containers that are connected to that network can access the alias.
In addition to the above features, multiple containers can share the same network-scoped
alias within the same network. For example, let's launch `container7` in `isolated_nw` with
the same alias as `container6`
```bash
$ docker run --net=isolated_nw -itd --name=container7 --net-alias app busybox
3138c678c123b8799f4c7cc6a0cecc595acbdfa8bf81f621834103cd4f504554
```
When multiple containers share the same alias, name resolution to that alias will happen
to one of the containers (typically the first container that is aliased). When the container
that backs the alias goes down or disconnected from the network, the next container that
backs the alias will be resolved.
Let us ping the alias `app` from `container4` and bring down `container6` to verify that
`container7` is resolving the `app` alias.
```bash
$ docker attach container4
/ # ping -w 4 app
PING app (172.25.0.6): 56 data bytes
64 bytes from 172.25.0.6: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.6: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=3 ttl=64 time=0.097 ms
--- app ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
$ docker stop container6
$ docker attach container4
/ # ping -w 4 app
PING app (172.25.0.7): 56 data bytes
64 bytes from 172.25.0.7: seq=0 ttl=64 time=0.095 ms
64 bytes from 172.25.0.7: seq=1 ttl=64 time=0.075 ms
64 bytes from 172.25.0.7: seq=2 ttl=64 time=0.072 ms
64 bytes from 172.25.0.7: seq=3 ttl=64 time=0.101 ms
--- app ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.072/0.085/0.101 ms
```
## Disconnecting containers