99 lines
3.8 KiB
ReStructuredText
99 lines
3.8 KiB
ReStructuredText
:title: Working with Links and Names
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:description: How to create and use links and names
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:keywords: Examples, Usage, links, docker, documentation, examples, names, name, container naming
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.. _working_with_links_names:
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Working with Links and Names
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============================
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From version 0.6.5 you are able to ``name`` a container and ``link`` it to another
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container by referring its name. This will create a relation parent->child where
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the parent container can see all the important information about its child.
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.. _run_name:
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Container Naming
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----------------
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.. versionadded:: v0.6.5
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You can now name your container by using ``-name`` flag. If no name is provided,
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Docker will automatically generate a name which can be seen by typing: ``docker ps``.
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.. code-block:: bash
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# format is "sudo docker run -name <container_name> <image_name> <command>"
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$ sudo docker run -name test ubuntu /bin/bash
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.. _run_link:
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Links: service discovery for docker
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-----------------------------------
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.. versionadded:: v0.6.5
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Links allow containers to discover and securely communicate with each other by using the
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flag ``-link name:alias``. Inter-container communication can be disabled with the daemon
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flag ``-icc=false``. With this flag set to false, Container A cannot access Container B
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unless explicitly allowed via a link. This is a huge win for securing your containers.
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When two containers are linked together Docker creates a parent child relationship
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between the containers. The parent container will be able to access information via
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env variables of the child such as name, exposed ports, ip, and environment variables.
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When linking two containers Docker will use the exposed ports of the container to create
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a secure tunnel for the parent to access. If a database container only exposes port 8080
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then the linked container will only be allowed to access port 8080 and nothing else if
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inter-container communication is set to false.
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.. code-block:: bash
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# Example: there is an image called redis-2.6 that exposes the port 6379 and starts redis-server.
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# Let's name the container as "redis" based on that image and run it as daemon.
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$ sudo docker run -d -name redis redis-2.6
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We can issue all the commands that you would expect using the name "redis"; start, stop,
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attach, using the name for our container. The name also allows us to link other containers
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into this one.
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Next, we can start a new web application that has a dependency on Redis and apply a link
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to connect both containers. If you noticed when running our Redis server we did not use
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the -p flag to publish the Redis port to the host system. Redis exposed port 6379 and
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this is all we need to establish a link.
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.. code-block:: bash
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# Linking the redis container as a child
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$ sudo docker run -t -i -link redis:db -name webapp ubuntu bash
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When you specified -link redis:db you are telling docker to link the container named redis
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into this new container with the alias db. Environment variables are prefixed with the alias
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so that the parent container can access network and environment information from the containers
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that are linked into it.
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If we inspect the environment variables of the second container, we would see all the information
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about the child container.
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.. code-block:: bash
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$ sroot@4c01db0b339c:/# env
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HOSTNAME=4c01db0b339c
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DB_NAME=/webapp/db
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TERM=xterm
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DB_PORT=tcp://172.17.0.8:6379
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DB_PORT_6379_TCP=tcp://172.17.0.8:6379
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DB_PORT_6379_TCP_PROTO=tcp
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DB_PORT_6379_TCP_ADDR=172.17.0.8
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DB_PORT_6379_TCP_PORT=6379
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PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
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PWD=/
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SHLVL=1
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HOME=/
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container=lxc
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_=/usr/bin/env
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root@4c01db0b339c:/#
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Accessing the network information along with the environment of the child container allows
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us to easily connect to the Redis service on the specific IP and port in the environment.
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