Passing extra environment variables¶

You can pass in or override arbitrary environment variables by providing a dictionary of environment variables key/value pairs. This can be done both at the service level and the container level; the latter taking precedence:

services:
  myservice:
    image: ...
    env:
      FOO: bar
    instance-1:
      ship: host
      env:
        FOO: overrides bar
        FOO_2: bar2

Additionally, Maestro will automatically expand all levels of YAML lists in environment variable values. The following are equivalent:

env:
  FOO: This is a test
  BAR: [ This, [ is, a ], test ]

This becomes useful when used in conjunction with YAML references to build more complex environment variable values:

_globals:
  DEFAULT_JVM_OPTS: &jvmopts [ '-Xms500m', '-Xmx2g', '-showversion', '-server' ]

...

env:
  JVM_OPTS: [ *jvmopts, '-XX:+UseConcMarkSweep' ]

Examples of Docker images with Maestro orchestration¶

For examples of Docker images that are suitable for use with Maestro, you can look at the following repositories:

http://github.com/signalfuse/docker-cassandra A Cassandra image. Nodes within the same cluster are automatically used as Gossip seed peers.
http://github.com/signalfuse/docker-elasticsearch ElasicSearch with ZooKeeper-based discovery instead of the multicast-based discovery, to work in cloud environments.
http://github.com/signalfuse/docker-zookeeper A ZooKeeper image, automatically creating a cluster with the other instances in the same environment.