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Dockerizing a Redis service

Very simple, no frills, Redis service attached to a web application using a link.

Create a Docker container for Redis

Firstly, we create a Dockerfile for our new Redis image.

FROM        ubuntu:14.04
RUN         apt-get update && apt-get install -y redis-server
EXPOSE      6379
ENTRYPOINT  ["/usr/bin/redis-server"]

Next we build an image from our Dockerfile. Replace <your username> with your own user name.

$ docker build -t <your username>/redis .

Run the service

Use the image we’ve just created and name your container redis.

Running the service with -d runs the container in detached mode, leaving the container running in the background.

Importantly, we’re not exposing any ports on our container. Instead we’re going to use a container link to provide access to our Redis database.

$ docker run --name redis -d <your username>/redis

Create your web application container

Next we can create a container for our application. We’re going to use the -link flag to create a link to the redis container we’ve just created with an alias of db. This will create a secure tunnel to the redis container and expose the Redis instance running inside that container to only this container.

$ docker run --link redis:db -i -t ubuntu:14.04 /bin/bash

Once inside our freshly created container we need to install Redis to get the redis-cli binary to test our connection.

$ sudo apt-get update
$ sudo apt-get install redis-server
$ sudo service redis-server stop

As we’ve used the --link redis:db option, Docker has created some environment variables in our web application container.

$ env | grep DB_

# Should return something similar to this with your values
DB_NAME=/violet_wolf/db
DB_PORT_6379_TCP_PORT=6379
DB_PORT=tcp://172.17.0.33:6379
DB_PORT_6379_TCP=tcp://172.17.0.33:6379
DB_PORT_6379_TCP_ADDR=172.17.0.33
DB_PORT_6379_TCP_PROTO=tcp

We can see that we’ve got a small list of environment variables prefixed with DB. The DB comes from the link alias specified when we launched the container. Let’s use the DB_PORT_6379_TCP_ADDR variable to connect to our Redis container.

$ redis-cli -h $DB_PORT_6379_TCP_ADDR
$ redis 172.17.0.33:6379>
$ redis 172.17.0.33:6379> set docker awesome
OK
$ redis 172.17.0.33:6379> get docker
"awesome"
$ redis 172.17.0.33:6379> exit

We could easily use this or other environment variables in our web application to make a connection to our redis container.