Examples¶

Launching Zookeeper¶

The zookeeper host in the cluster is expected to be named zk01 and use the standard ports, so it can be launched with:

$ docker run --name zk01 -d lighthouse.examples.zk

Launching a Client¶

Launching a client container is a simple matter of using the included launch.sh helper script found in the examples directory:

$ ./launch.sh client client

Details about the script can be found in the launching section.

Launching¶

Launching a new node can be done by hand via docker, but the examples directory includes a handy launch.sh script to make things easier:

$ ./launch.sh <type> <name>

Where the “<type>” matches the end of the example docker image name. For example the “lighthouse.examples.webapp” image’s node type is “webapp”.

The “<name>” portion is any host name you want to give to the node. Since this is an SOA and nodes are (hopefully) automatically discovered the name doesn’t really matter and is mostly for convenience.

Examining¶

Each node container exposes two web interface ports for examining what exactly is going on: one for HAProxy and one for Supervisord, the process management tool used to run multiple processes at once in a single container. The HAProxy web interface listens on port 9009 with the URI “/haproxy”, the supervisord web interface listens on port 9000.

To avoid conflicting port assignments, a container will map these ports to a random available one on the docker host. To see the resulting mapped port you’ll have to run docker ps:

$ docker ps

CONTAINER ID        IMAGE                              COMMAND                CREATED             STATUS              PORTS                                                                                                NAMES
aa037622260e        lighthouse.examples.cache:latest   "/bin/sh -c 'supervi   3 seconds ago       Up 2 seconds        0.0.0.0:32768->1024/tcp, 0.0.0.0:32769->6379/tcp, 0.0.0.0:32770->9000/tcp, 0.0.0.0:32771->9009/tcp   cache01
85890f46dc8f        lighthouse.examples.zk:latest      "/opt/zookeeper/bin/   17 seconds ago      Up 16 seconds       2181/tcp, 2888/tcp, 3888/tcp                                                                         zk01

In this example, the “cache01” container’s HAProxy web interface can be accessed via http://<docker_host_ip>:32771/haproxy and the supervisord web interface via http://<docker_host_ip>:32770.

Connecting¶

Along with the launch.sh script there’s also a handy connect.sh script:

$ ./connect.sh <name>

This will attach to the container with the “<name>” name and run an interactive bash session, helpful for examining log and configuration files by hand. Note that the TERM environment variable is not set by default so many things like less and clear might not work quite right unless it’s set by hand.

For each node the lighthouse scripts run in debug mode and log quite a bit. The log files for the lighthouse script live under /var/log/supervisor/lighthouse in the container. The services served up by containers will generally put their logs under /var/log/supervisor/.

The HAProxy config is written to /etc/haproxy.cfg.

Stopping¶

Unlike launching or connecting, there is no helper script as a simple docker command does the job:

$ docker rm -f <name>

This will halt the node container and unregister it from zookeeper automatically.