cassandra-docker

Dockerfile & scripts to run Cassandra in Docker

Running

A Docker image with Datastax Community Edition / Cassandra 2.0.8 is published to tobert/dsc208. It expects a volume to be assigned. This volume will be written to!

docker pull tobert/dsc208
mkdir /srv/cassandra
docker run -d -v /srv/cassandra:/var/lib/cassandra tobert/dsc208

Building

sudo docker build -t dsc208 .

Running a Single Node

While it is possible to run a node without a volume attached, this is not recommended. Most COW filesystems used by Docker will not perform well under database workloads.

docker run -v /var/lib/cassandra dsc208

With SSH

Note: the ssh support will probably go away soon (to be replaced by nsenter).

When the container starts up, cassandra-runner.pl will automatically start a dropbear ssh daemon. Since it binds by IP you can find the IP in ps output or more accurately by looking at $VOLUME/etc/listen_address.txt

One way to get an authorized_keys file into the container is with a volume. Using your ~/.ssh/authorized_keys works fine like this.

The other way is to create an authorized_keys file in $VOLUME/etc/authorized_keys before booting and it will get copied to /root/.ssh for you.

docker run -v $HOME/.ssh:/root/.ssh:ro -v /var/lib/cassandra dsc208
ssh root@$(cat /var/lib/cassandra/etc/listen_address.txt)

Running a Cluster

The whole point of this config is to make it easy to run clusters on a single machine for development purposes. The trickiest part is getting the seed into following nodes. This can be done without modifying images, as the wrapper script will take care of editing the configuration for you if you pass in the SEEDS environment variable.

Setting a memory limit is also important for clusters since Cassandra will happily eat up 50% of RAM for each instance unless you limit it.

mkdir -p /var/lib/{cass1,cass2,cass3}
docker run -d -m 1500m -v /var/lib/cass1:/var/lib/cassandra tobert/dsc208
sleep 5
# get the IP of the new container
IP=$(< /var/lib/cass1/etc/listen_address.txt)
docker run -d -m 1500m -e SEEDS=$IP -v /var/lib/cass2:/var/lib/cassandra tobert/dsc208
docker run -d -m 1500m -e SEEDS=$IP -v /var/lib/cass3:/var/lib/cassandra tobert/dsc208
nodetool -h $IP status

Advanced Configuration

There are a few ways to get more control over the Cassandra instance without messing with the Docker image.

Setting JVM Memory Usage

Option A: set the MAX_HEAP_SIZE and HEAP_NEWSIZE environment variables. These must be acceptable values for -Xmx and -Xmn respectively. They will be persisted in the volume under etc/env.sh automatically, so these flags are only required the first time.

docker run -m 2g -e MAX_HEAP_SIZE=1G -e HEAP_NEWSIZE=200M -v /var/lib/cass1:/var/lib/cassandra dsc208

Option B: create a env.sh file in the state dir, which is the etc directory under your volume.

cat > /var/lib/cass1/etc/env.sh <<EOF
MAX_HEAP_SIZE=1500M
HEAP_NEWSIZE=256M
EOF
docker run -d -m 2g -v /var/lib/cass1:/var/lib/cassandra dsc208