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Node.js Runtime

This reference summarizes practical runtime defaults for Node.js workloads on Azure Container Apps so you can keep startup behavior, probe health, and logging predictable across revisions.

Runtime Execution Model

flowchart TD
    IMG[Container Image] --> BOOT[Node.js Startup]
    BOOT --> PORT[Bind 0.0.0.0:8000]
    PORT --> PROBE[Health Probes]
    PROBE --> TRAFFIC[Ingress Traffic]
    TRAFFIC --> LOGS[stdout/stderr to Log Analytics]

Treat runtime settings as deployment contracts

Keep port binding, process model, and logging behavior stable between revisions. Changing all three at once makes incident triage much harder.

Runtime Baseline (This Repo)

Item Value
Base image node:20-slim
Web framework Express
Process manager Node.js (native)
Exposed/listen port 8000
Start command node src/app.js

Node.js Memory Management

When running Node.js in containers, it's important to align the V8 heap size with the container memory limit.

Setting Example When to change
Max Heap Size --max-old-space-size=1536 Set to ~75% of container memory (e.g., 1.5GB for 2GB container)
HTTP Keep-Alive server.keepAliveTimeout = 65000 Increase to match or exceed Azure Ingress timeouts (60s)
Graceful Shutdown server.close() Ensure SIGTERM is handled to finish in-flight requests 
# In Dockerfile
CMD ["node", "--max-old-space-size=1536", "src/app.js"]

Container Apps Alignment Checklist

Check Expected
Azure Container Apps targetPort 8000
Express bind 0.0.0.0:8000
Health endpoint GET /health returns 200
Logs stdout/stderr JSON format
Secrets/config Read from process.env

Quick Diagnostics

RG="rg-nodejs-guide"

# For CLI-deployed apps, set directly:
# APP_NAME="ca-nodejs-guide"

# For Bicep-deployed apps, capture from outputs:
DEPLOYMENT_NAME="main"
APP_NAME=$(az deployment group show \
  --name "$DEPLOYMENT_NAME" \
  --resource-group "$RG" \
  --query "properties.outputs.containerAppName.value" \
  --output tsv)

az containerapp logs show \
  --name "$APP_NAME" \
  --resource-group "$RG" \
  --type console --follow

az containerapp exec \
  --name "$APP_NAME" \
  --resource-group "$RG" \
  --command "/bin/sh"

# Inside container
node --version
npm list --depth=0
ps aux
Command Purpose
APP_NAME=$(az deployment group show --name "$DEPLOYMENT_NAME" --resource-group "$RG" --query "properties.outputs.containerAppName.value" --output tsv) Pulls the deployed Node.js app name from the Bicep outputs so the runtime checks target the exact app created by the guide.
az containerapp logs show --name "$APP_NAME" --resource-group "$RG" --type console --follow Streams the app's console logs so you can inspect Express startup and request logs in real time.
az containerapp exec --name "$APP_NAME" --resource-group "$RG" --command "/bin/sh" Opens a shell inside the running container so you can verify the Node.js runtime, installed packages, and active processes from the replica itself.

Frequent Runtime Failures

Symptom Root cause Action
Container healthy locally, failing in Container Apps Port/ingress mismatch Align Express bind and Container Apps targetPort
Memory leaks or OOM kills V8 heap exceeds container limit Set --max-old-space-size and check for leaks
Requests dropped during rollout Missing SIGTERM handler Implement graceful shutdown in src/app.js
Missing logs in Log Analytics Console output not captured Ensure logs are written to stdout/stderr, not files

Avoid hardcoding runtime assumptions

If your app assumes a fixed port, writable local filesystem, or shell-only startup dependencies, revisions may pass locally but fail in Container Apps. Validate behavior with environment-driven configuration and health probes.

See Also

Sources