Removed redundant linking example
This commit is contained in:
James Turnbull
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1182797c6d
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@ -24,4 +24,3 @@ to more substantial services like those which you might find in production.
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postgresql_service
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postgresql_service
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mongodb
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mongodb
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running_riak_service
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running_riak_service
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linking_into_redis
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@ -1,137 +0,0 @@
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:title: Linking to an Redis container
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:description: Running redis linked into your web app
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:keywords: docker, example, networking, redis, link
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.. _linking_redis:
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Linking Redis
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=============
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.. include:: example_header.inc
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Building a Redis container to link as a child of our web application.
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Building the Redis container
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----------------------------
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Lets build a Redis image with the following Dockerfile.
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First checkout the Redis source code.
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.. code-block:: bash
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git clone https://github.com/antirez/redis.git
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cd redis
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git checkout 2.6
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Now let's create a Dockerfile in the root of the Redis repository.
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.. code-block:: bash
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# Build redis from source
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# Make sure you have the redis source code checked out in
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# the same directory as this Dockerfile
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FROM ubuntu
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RUN echo "deb http://archive.ubuntu.com/ubuntu precise main universe" > /etc/apt/sources.list
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RUN apt-get update
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RUN apt-get upgrade -y
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RUN apt-get install -y gcc make g++ build-essential libc6-dev tcl
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ADD . /redis
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RUN (cd /redis && make)
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RUN mkdir -p /redis-data
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VOLUME ["/redis-data"]
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EXPOSE 6379
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ENTRYPOINT ["/redis/src/redis-server"]
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CMD ["--dir", "/redis-data"]
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# docker build our new redis image from source
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docker build -t redis-2.6 .
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We need to ``EXPOSE`` the default port of 6379 so that our link knows what ports
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to connect to our Redis container on. If you do not expose any ports for the
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image then docker will not be able to establish the link between containers.
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Run the Redis container
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-----------------------
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.. code-block:: bash
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sudo docker run -d -e PASSWORD=docker -name redis redis-2.6 --requirepass docker
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This will run our Redis container with the password docker
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to secure our service. By specifying the ``-name`` flag on run
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we will assign the name ``redis`` to this container. If we do not specify a name for
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our container via the ``-name`` flag docker will automatically generate a name for us.
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We can issue all the commands that you would expect; start, stop, attach, using the name for our container.
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The name also allows us to link other containers into this one.
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Linking Redis as a child
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------------------------
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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 via the Dockerfile
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and this is all we need to establish a link.
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Now let's start our web application with a link into Redis.
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.. code-block:: bash
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sudo docker run -t -i -link redis:db -name webapp ubuntu bash
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root@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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DB_ENV_PASSWORD=docker
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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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When we inspect the environment of the linked container we can see a few extra environment
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variables have been added. When you specified ``-link redis:db`` you are telling docker
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to link the container named ``redis`` into this new container with the alias ``db``.
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Environment variables are prefixed with the alias so that the parent container can access
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network and environment information from the containers that are linked into it.
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.. code-block:: bash
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# The name of the child container
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DB_NAME=/webapp/db
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# The default protocol, ip, and port of the service running in the container
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DB_PORT=tcp://172.17.0.8:6379
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# A specific protocol, ip, and port of various services
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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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# Get environment variables of the container
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DB_ENV_PASSWORD=docker
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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 and use the password
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specified in the environment.
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