Using env variables in kong.yml with Kong and Docker-compose

Question

I am trying to use Kong in declarative way with a kong.yml file. I want to be able to use environment variables in the kong.yml file. I have the following content in my docker-compose:

kong: 
    image: kong:2.7.0-alpine
    restart: "always"
    hostname: kong
    container_name: kong
    networks:
      - kong-net
    environment:
      KONG_DATABASE: "off"
      KONG_PROXY_ACCESS_LOG: /dev/stdout
      KONG_PROXY_ERROR_LOG: /dev/stderr
      KONG_ADMIN_ACCESS_LOG: /dev/stdout
      KONG_ADMIN_ERROR_LOG: /dev/stderr
      KONG_ADMIN_LISTEN: "0.0.0.0:8001, 0.0.0.0:8444 ssl"
      KONG_DECLARATIVE_CONFIG: "/opt/kong/kong.yml"
      ADMIN_MICROSERVICE_PORT: ${ADMIN_MICROSERVICE_PORT}
      REPORTING_MICROSERVICE_PORT: ${REPORTING_MICROSERVICE_PORT}
      INTERNAL_IP: ${INTERNAL_IP}
    command: "kong start --v"
    ports: 
      - "${INTERNAL_IP}:8000:8000"
      - "${INTERNAL_IP}:8443:8443"
      - "${INTERNAL_IP}:8001:8001"
      - "${INTERNAL_IP}:8444:8444"
    volumes:
      - ./kong/config:/opt/kong

And a kong.yml file:

_format_version: "2.1"
_transform: true


services:
- name: controllers
  url: https://${INTERNAL_IP}:${ADMIN_MICROSERVICE_PORT}
  routes:
  - name: controller-routes
    paths:
    - /admin/controllers 

- name: vpnprofiles
  url: https://${INTERNAL_IP}:${ADMIN_MICROSERVICE_PORT}
  routes:
  - name: vpnprofiles-routes
    paths:
    - /admin/vpnprofiles

- name: device_report
  url: https://${INTERNAL_IP}:${REPORTING_MICROSERVICE_PORT}
  routes:
  - name: device-report-routes
    paths:
    - /reporting/device_report

Here are the logs of the kong image:

022/01/01 12:38:46 [error] 1095#0: init_by_lua error: /usr/local/share/lua/5.1/kong/init.lua:551: error parsing declarative config file /opt/kong/kong.yml:
in 'services':
  - in entry 1 of 'services':
    in 'host': invalid value: ${INTERNAL_IP}
    in 'port': expected an integer
  - in entry 2 of 'services':
    in 'host': invalid value: ${INTERNAL_IP}
    in 'port': expected an integer
  - in entry 3 of 'services':
    in 'host': invalid value: ${INTERNAL_IP}
    in 'port': expected an integer
stack traceback:
    [C]: in function 'error'
    /usr/local/share/lua/5.1/kong/init.lua:551: in function 'init'
    init_by_lua:3: in main chunk

However, variables in kong.yml are not substituted at launch. Am I doing something wrong ?

I don't think it directly supports expanding environment variables in the config file. There appears to be some override support for KONG_ prefixed variables, but my understanding of kong internals is limited to know if, perhaps KONG_SERVICES_CONTROLLERS_URL might be used to set that first value — Anya Shenanigans, Jan 01 '22 at 12:45

Using env variables in kong.yml with Kong and Docker-compose

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