Resources and replicas

Say how much CPU and memory a service needs, and how many copies of it run.

You declareThe platform generates

compose.production.yaml

services:
  web:
    deploy:
      replicas: 2 # (1)!
      resources:
        reservations: # (2)!
          cpus: "0.1"
          memory: 320M
        limits: # (3)!
          cpus: "1"
          memory: 1G

1. How many copies run.
2. What the service needs to run.
3. The most it may use.

Generated on every release. You never write this file or see it. Sizes are written in bytes: 1G is 1073741824.

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    com.docker.compose.project: my-app
    com.docker.compose.service: web
  name: web
  namespace: my-app
spec:
  replicas: 2 # (1)!
  selector:
    matchLabels:
      com.docker.compose.project: my-app
      com.docker.compose.service: web
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        com.docker.compose.project: my-app
        com.docker.compose.service: web
        com.docker.compose.network.default: 'true'
    spec:
      containers:
      - image: my-app:local
        imagePullPolicy: IfNotPresent
        name: web
        resources:
          limits: # (2)!
            cpu: '1'
            memory: '1073741824'
          requests: # (3)!
            cpu: '0.1'
            memory: '335544320'

1. Your deploy.replicas.
2. Your limits. Memory in bytes.
3. Your reservations.

Each environment's file carries its own budget.

Make sure your application is stateless

Copies do not share memory, and a copy can be replaced at any time. Keep sessions, uploads, and any other state in a database, a cache, or a bucket.

Fields

Field	Default	Values
deploy.replicas	1	An integer, 0 or more
deploy.resources.reservations.cpus		CPUs, such as "0.1"
deploy.resources.reservations.memory		A size, such as 320M or 1G
deploy.resources.limits.cpus		CPUs, such as "1"
deploy.resources.limits.memory		A size, such as 320M or 1G

Every field is optional and independent. A value you omit is not set.

What you get

On your machine

Behavior	Detail
Copies	Docker starts as many containers as replicas says
Limits	A container cannot use more CPU or memory than its limits
Memory reservation	Applied as a soft limit
CPU reservation	Has no effect on your machine. It only counts on the cluster

On the cluster

The cluster places each copy where its reservations fit and holds it to its limits. It runs as many copies as replicas says. You write no manifest.

Rules

Rule	Detail
Only CPU and memory	Other entries under reservations or limits, such as devices and pids, are rejected
scale agrees with replicas	If a service declares both, they hold the same number
A scheduled job has one copy	See Scheduled jobs
deploy reads replicas and resources	Any other field under deploy is rejected