Docker Compose read common environment variables <<

Question

I am working on a shared project, that contains a docker compose file with structure as below. (Confidential info removed)

version: "3.9"
# https://docs.docker.com/compose/compose-file/

x-common-variables: &common-variables
  JAVA_TOOL_OPTIONS: -XX:MaxRAMPercentage=60.0 -Dlogging.level.com.backbase=DEBUG
  ... More common variables

x-database-variables: &database-variables
  spring.liquibase.enabled: true
  ... More DB Variables

x-message-broker-variables: &message-broker-variables
  spring.activemq.broker-url: tcp://message-broker:61616
  ... More message broker variables

x-healthcheck-defaults: &healthcheck-defaults
  start_period: 60s
  ... more defaults

services:
  mysql:
    ... More details

  message-broker:
    ... More details


  serviceName:
    container_name: containerName
    image: imagePath
    ports:
      - "8080:8080"
    environment:
    // Following line works
      <<: *common-variables
      
   

  another-service:
    container_name: another-container
    image: another-image-path
    ports:
      - "8040:8080"
    environment:
      <<: *common-variables
       // BREAKS HERE
      <<: *message-broker-variables
      <<: *database-variables

The ingestion of variables via "<<" works for one service, but breaks for another with the following

line 138: mapping key "<<" already defined at line 137

I am using docker version

Docker version 24.0.2-rd, build e63f5fa
colima version 0.5.4
git commit: feef4176f56a7dea487d43689317a9d7fe9de27e

runtime: docker
arch: x86_64
client: v24.0.2-rd
server: v20.10.20

The same file works on other dev machines (I am not sure of their config). Kindly suggest what could be the cause of this issue?

Don't just strip out random parts, extract a [mcve] instead. — Ulrich Eckhardt, Aug 05 '23 at 08:50
`<<:` isn't syntactically special; it is a map key `<<` that has a special value. You can only use `<<:` once in a given YAML map, but it can have a list value `<<: [*common-variables, *message-broker-variables, *database-variables]`. — David Maze, Aug 05 '23 at 10:22

score 0 · Answer 1 · answered Aug 05 '23 at 05:15

I was not able to find an appropriate answer. I am still looking for an answer, however below is the workaround I am using.

I manually replaced all the environment variables that it was trying to import by << command.

This means duplicate code, and additional effort while merging the code. But at least it works.

Docker Compose read common environment variables <<

1 Answers1