Configuration files

Give a service a file from your repository. It reads it at the path you choose.

You declareThe platform generates

compose.yaml

services:
  caddy:
    image: caddy:2
    configs:
      - source: caddyfile # (1)!
        target: /etc/caddy/Caddyfile # (2)!

configs:
  caddyfile:
    file: caddy/Caddyfile # (3)!

1. The file this service may read.
2. Where the service finds it.
3. A file in your repository, in plain text.

Generated on every release. You never write these files or see them.

apiVersion: v1
data:
  content: ":80 {\n    reverse_proxy web:8000\n}\n" # (1)!
kind: ConfigMap
metadata:
  labels:
    com.docker.compose.project: my-app
  name: caddyfile
  namespace: my-app

1. Your file, as text. A binary file travels as binaryData.

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    com.docker.compose.project: my-app
    com.docker.compose.service: caddy
  name: caddy
  namespace: my-app
spec:
  replicas: 1
  selector:
    matchLabels:
      com.docker.compose.project: my-app
      com.docker.compose.service: caddy
  strategy:
    type: Recreate
  template:
    metadata:
      annotations:
        checksum/configs: 45763d4691d7a9e3e75325550f14bddf2b791ce655e7c330ac4d8bc65ddb64cb # (1)!
      labels:
        com.docker.compose.project: my-app
        com.docker.compose.service: caddy
        com.docker.compose.network.default: 'true'
    spec:
      containers:
      - image: caddy:2
        imagePullPolicy: IfNotPresent
        name: caddy
        volumeMounts:
        - mountPath: /etc/caddy/Caddyfile # (2)!
          name: config-0
          readOnly: true
          subPath: content
      volumes:
      - configMap:
          items:
          - key: content
            mode: 292 # (3)!
            path: content
          name: caddyfile
        name: config-0

1. Changes with the file. A new value restarts the service.
2. Your target.
3. 0444: the file is read only.

A config is for public files: a Caddyfile, a script, a logo. A credential goes in Secrets.

Fields

Field	Required	Default	Values
configs[].source	Yes		The name of a config declared at the top
configs[].target	No	/<source>	An absolute path to the file inside the container
configs[].mode	No	0444	Permissions of the file
configs.<name>.file	Yes		A file in your repository, text or binary

What you get

On your machine

Behavior	Detail
The file from your repository	Docker mounts it at target, read only
Edit and restart	Change the file in your repository and start the stack again

On the cluster

Behavior	Detail
A copy travels with the release	The file is read when the release is built
Read only	The service cannot change it
A change restarts the readers	A new content restarts the services that read the file, and no other

Rules

Rule	Detail
A config comes from a file	file is required. content and external are rejected
Up to 1 MiB	A bigger file is rejected
One file, one path	target is an absolute file path. Two files cannot share it, and a config cannot cover a secret
No owner per file	uid and gid other than 0 are rejected