Using Redis as Tomcat Session Store with Docker

02 January 2015

This is the first part of a series of posts on how to create a scalable Java Application with Docker. TDD and Integration Tests helps us a lot to have some trust in our source code. Amongst other things, Docker helps us to have more trust in our applications as a whole, by running whole applications in a production-like cluster setup on a single host. In this initial post I will prepare a Tomcat Docker Image which uses Redis as a Session Store, which we can use in later posts to achive high availability for our user sessions.

Start a Redis Server

To start a Redis server simply start the official Redis Docker Image.

docker run -d --name redis-session-store redis

Now verify that the Redis server is working properly.

docker run -it --link redis-session-store:redis --rm redis sh -c 'exec redis-cli -h "$REDIS_PORT_6379_TCP_ADDR" -p "$REDIS_PORT_6379_TCP_PORT"'
172.17.0.5:6379> INFO keyspace
# Keyspace

You should now be logged in to your Redis Server. When typing INFO keyspace, no surprise, there is no keyspace yet.

Prepare the Tomcat Image

To use Redis as the Session Store, a Session Manager Implementation is required. Luckily a project called tomcat-redis-session-manager exists, which provides an implementation. The latest official release of the project is quite old, so I forked it and added a compiled jar of the master branch on Github. As Tomcat base image I have used tutum/tomcat:7.0. Next the Session Manager and its dependencies needed to be placed in the image:

RUN \
    cd /tomcat/lib && \
    wget -q  https://github.com/rmohr/tomcat-redis-session-manager/releases/download/2.0-tomcat-7/tomcat-redis-session-manager-2.0.0.jar && \
    wget -q http://central.maven.org/maven2/redis/clients/jedis/2.5.2/jedis-2.5.2.jar && \
    wget -q http://central.maven.org/maven2/org/apache/commons/commons-pool2/2.2/commons-pool2-2.2.jar

For convenience the two environment variables REDIS_HOST and REDIS_PORT were added to the Dockerfile. They will be evalueted on runtime. Default values are redis and 6379, which are sufficient when linking the containers correctly.

ENV REDIS_HOST redis # Redis server host name
ENV REDIS_PORT 6379 # Redis server port

Start the Tomcat Image

Luckily I have created a rmohr/tomcat-redis Trusted Build Image with the Session Manager built-in. You can see the Dockerfile on Github. To start the Image and link it against the Redis Image, simply run

docker run --link redis-session-store:redis -p 8080:8080 rmohr/tomcat-redis:7.0
=> Creating and admin user with a random password in Tomcat
=> Done!
========================================================================
You can now configure to this Tomcat server using:

    admin:XPkpXKB8yuzS

========================================================================

Got to http://localhost:8080/manager/html and log in with the credentials you see on the Tomcat container output. Finally login to the Redis Server again and do the following:

$ docker run -it --link redis:redis --rm redis sh -c 'exec redis-cli -h "$REDIS_PORT_6379_TCP_ADDR" -p "$REDIS_PORT_6379_TCP_PORT"'
172.17.0.5:6379> INFO keyspace
# Keyspace
db0:keys=1,expires=1,avg_ttl=1696125
172.17.0.5:6379> KEYS '*'
1) "C83B106DBE9E5CB28EEC7E0B463628E1"
172.17.0.5:6379> GET "C83B106DBE9E5CB28EEC7E0B463628E1"
"\xac\xed\x00\x05sr\x00Dcom.orangefunction.tomcat.redissessions.SessionSerializationMetadataB\xd9\xd9\xf7v\xa2\xdbL\x03\x00\x01[\x00\x15sessionAttributesHasht\x00\x02[Bxpw\x14\x00\x00\x00\x10tcon?\xc1\xaa\x827\x99\x0by\x93=|\xcdxsr\x00\x0ejava.lang.Long;\x8b\xe4\x90\xcc\x8f#\xdf\x02\x00\x01J\x00\x05valuexr\x00\x10java.lang.Number\x86\xac\x95\x1d\x0b\x94\xe0\x8b\x02\x00\x00xp\x00\x00\x01J\xab{h\xb4sq\x00~\x00\x03\x00\x00\x01J\xab{h\xb4sr\x00\x11java.lang.Integer\x12\xe2\xa0\xa4\xf7\x81\x878\x02\x00\x01I\x00\x05valuexq\x00~\x00\x04\x00\x1bw@sr\x00\x11java.lang.Boolean\xcd r\x80\xd5\x9c\xfa\xee\x02\x00\x01Z\x00\x05valuexp\x00sq\x00~\x00\t\x01sq\x00~\x00\x03\x00\x00\x01J\xab}\x91\xa3t\x00 C83B106DBE9E5CB28EEC7E0B463628E1sq\x00~\x00\a\x00\x00\x00\x01t\x00&org.apache.catalina.filters.CSRF_NONCEsr\x009org.apache.catalina.filters.CsrfPreventionFilter$LruCache\x00\x00\x00\x00\x00\x00\x00\x01\x02\x00\x01L\x00\x05cachet\x00\x0fLjava/util/Map;xpsr\x00;org.apache.catalina.filters.CsrfPreventionFilter$LruCache$1\x00\x00\x00\x00\x00\x00\x00\x01\x02\x00\x02I\x00\rval$cacheSizeL\x00\x06this$0t\x00;Lorg/apache/catalina/filters/CsrfPreventionFilter$LruCache;xr\x00\x17java.util.LinkedHashMap4\xc0N\\\x10l\xc0\xfb\x02\x00\x01Z\x00\x0baccessOrderxr\x00\x11java.util.HashMap\x05\a\xda\xc1\xc3\x16`\xd1\x03\x00\x02F\x00\nloadFactorI\x00\tthresholdxp?@\x00\x00\x00\x00\x00\x00w\b\x00\x00\x00\x01\x00\x00\x00\x01t\x00 AD33B7B7EC4106A74733738E12E8FAD2px\x00\x00\x00\x00\x05q\x00~\x00\x12w\b\x00\x00\x01J\xab{h\xb4"

Tomcat successfully stored the Session in Redis.

A minimal Fig setup with persistence for Redis enabled might look like this:

redis:
    image: redis
    volumes:
        - ./data:/data

tomcat:
    image: rmohr/tomcat-redis:7.0
    ports:
        - 8080:8080 
    links:
        - redis:redis

In the next post I will show you, how to configure Redis and the Tomcat Image to use Redis Sentinel, for achieving automatic failover.

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