Deploy a Node.js service

This recipe deploys a minimal Express service whose configuration comes from a Rune configmap via envFrom. The image stays generic; the environment owns the config.

Full source: runestack/rune-examples/node-express.

The app

One endpoint that reads its greeting from the environment, plus a health endpoint:

import express from 'express'
import os from 'node:os'
 
const app = express()
 
// GREETING comes from a Rune configmap via envFrom (see deploy/app.yaml).
const greeting = process.env.GREETING ?? 'hello from node on rune'
 
app.get('/api/hello', (req, res) => {
  res.json({ message: greeting, instance: os.hostname() })
})
 
app.get('/healthz', (req, res) => {
  res.send('ok')
})
 
app.listen(process.env.PORT ?? 3000)

The spec

Two resources in one castfile: the configmap and the service that consumes it. envFrom turns every key in the configmap into an environment variable, and the dependency makes the rollout wait until the configmap exists:

---
configmap:
  name: node-hello-settings
  namespace: demo
  data:
    GREETING: hello from node on rune
---
service:
  name: node-hello
  namespace: demo
  image: node-hello:dev
  scale: 2
  ports:
    - name: http
      port: 3000
  dependencies:
    - configmap:node-hello-settings
  envFrom:
    - configmap: node-hello-settings
  health:
    liveness:
      type: http
      path: /healthz
      port: 3000
      initialDelaySeconds: 2
      intervalSeconds: 10
  expose:
    port: http
    host: node-hello.local

Cast it

git clone https://github.com/runestack/rune-examples
cd rune-examples/node-express
 
docker build -t node-hello:dev ./app
rune lint deploy/app.yaml
rune cast deploy/app.yaml

echo "127.0.0.1 node-hello.local" | sudo tee -a /etc/hosts
 
curl http://node-hello.local/api/hello
# {"message":"hello from node on rune","instance":"87f68dc74039"}

In dev mode the ingress binds :8080, so use http://node-hello.local:8080.

Change config without rebuilding

Update the configmap and roll the service — the new value arrives as an env var on the next instance start. No image rebuild, no spec change:

rune create config node-hello-settings -n demo \
  --from-literal=GREETING="howdy from a configmap"
rune restart node-hello -n demo
 
curl http://node-hello.local/api/hello
# {"message":"howdy from a configmap","instance":"3c9d01ab54e2"}

Rune does not hot-reload env vars or mounted files — the restart is what picks up the new version. See Secrets & ConfigMaps.

rune delete -f deploy/app.yaml    # tear down

Adapting

Anything that reads config from the environment — which is to say, any twelve-factor app — works the same way: FastAPI, Rails, Spring. For sensitive values, use a secret instead of a configmap; the service side is the same shape (envFrom: - secret: name). For a full stack with a database and secrets, see Deploy Spring Boot + React.