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Combine Compose Files

In the prior example, we had 2 components that ran as servers: MySql and the Ruby Server.

The Java Data Load program is an initialization task.

Our stack would be more flexible if we were separate these components into 2 different files.

Component Files

These 2 compose files comprise the system that we have been testing.

• examples/session2/servers.yml
• examples/session2/loader.yml

Run docker-compose config to view a combined configuration file:

docker-compose \
  -f examples/session2/servers.yml \
  -f examples/session2/loader.yml \
  config

Note that all 3 containers are defined in the combined configuration

docker-compose \
  -f examples/session2/servers.yml \
  -f examples/session2/loader.yml \
  config | egrep 'image:'

    image: my-java
    image: my-mysql
    image: myruby

It is possible to overlay configuration overrides for specific containers.

• examples/session2/environment.yml
• examples/session2/environment-override.yml

Include environment.yml

docker-compose \
  -f examples/session2/servers.yml \
  -f examples/session2/loader.yml \
  -f examples/session2/environment.yml \
  config 

Search for HELLO/HOWDY in the combined config

docker-compose \
  -f examples/session2/servers.yml \
  -f examples/session2/loader.yml \
  -f examples/session2/environment.yml \
  config | egrep 'HELLO|HOWDY'

Note that the environment variable HELLO has been added to each container

      HELLO: sample message for data-load
      HELLO: sample message for mydb
      HELLO: sample message for ruby server

Add environment-override.yml to the configuration

docker-compose \
  -f examples/session2/servers.yml \
  -f examples/session2/loader.yml \
  -f examples/session2/environment.yml \
  -f examples/session2/environment-override.yml \
  config | egrep 'HELLO|HOWDY'

Note that the values have been overridden for HELLO and HOWDY for mydb

      HELLO: sample message for data-load
      HELLO: override value for mydb
      HOWDY: new value for mydb
      HELLO: sample message for ruby server

Switch the order of environment.yml and environment-override.yml.

docker-compose \
  -f examples/session2/servers.yml \
  -f examples/session2/loader.yml \
  -f examples/session2/environment-override.yml \
  -f examples/session2/environment.yml \
  config | egrep 'HELLO|HOWDY'

Note that the last value for HELLO is retained.

      HELLO: sample message for data-load
      HELLO: sample message for mydb
      HOWDY: new value for mydb
      HELLO: sample message for ruby server

When multiple compose files are combined, the results are MERGED.

For hash objects like environment variables, values can be overridden, but keys cannot be removed when combining properties.

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