dc-check

Simple Go Template syntax checker for Rancher's docker-compose files

Introduction

Rancher allows to use Go's template engine for docker-compose files. If you develop for a Rancher catalog item you might want to check how your docker-compose files look like based on possible answers given when you deploy a service from the catalog.

But how can you check how your docker-compose file looks like without actually deploying it?

Rancher deploys your file regardless whether Go Template engine has fully comiled your file or not. What's more, it's hard to interprete Rancher deployment errors if your file has newline or indentation errors and you can't actually see the resulting code.

This is where dc-check comes into play. It will just print the resulting docker-compose file to the console. See examples below.

Build

go build -o dc-check

Examples

A common example is to make ports public available or to just expose them internally.

mini-compose.yml:

{{- if eq .Values.PLAINTEXT_PORT_PUBLIC "true" }}
  ports:
  - 80:8080/tcp
{{- else }}
  expose:
  - 8080/tcp
{{- end }}

Example 1:

Setup your environment:

export PLAINTEXT_PORT_PUBLIC=true

./dc-check mini-compose.yml

will result in:

ports:
- 80:8080/tcp

Example 2:

Setup your environment:

export PLAINTEXT_PORT_PUBLIC=true

./dc-check mini-compose.yml

will result in:

expose:
- 8080/tcp

More examples

More complex example with ports can be found in this repo which also works if no port is public at all:

. sample1.env && ./dc-check sample-compose.yml

version: '2'
services:
  myservice:
    image: ubuntu:latest
    ports:
    - ${SSL_PORT}:8443/tcp
    expose:
    - 8080/tcp
    environment:
      LOGLEVEL: ${LOGLEVEL}

. sample2.env && ./dc-check sample-compose.yml

version: '2'
services:
  myservice:
    image: ubuntu:latest
    expose:
    - 8080/tcp
    - 8443/tcp
    environment:
      LOGLEVEL: ${LOGLEVEL}

. sample3.env && ./dc-check sample-compose.yml

version: '2'
services:
  myservice:
    image: ubuntu:latest
    ports:
    - ${PLAINTEXT_PORT}:8080/tcp
    - ${SSL_PORT}:8443/tcp
    environment:
      LOGLEVEL: ${LOGLEVEL}