Cloud Foundry Architecture Essentials

Component Breakdown

Key CF components include:

  • Diego: The container orchestration system
  • BOSH: Infrastructure and VM management
  • Router (Gorouter): Manages traffic to apps
  • Cloud Controller: Orchestrates deployments and app states

Each layer has unique logs, failure points, and dependencies, which must be traced precisely during debugging.

Deployment Topology

CF can be deployed on IaaS platforms like AWS, GCP, Azure, or OpenStack. Performance and error visibility vary by infrastructure quality, network latency, and log shipping reliability.

Common Failure Scenarios in Cloud Foundry

1. Application Crash Loop

Symptoms include repeated restarts and crash status in cf apps output. Common root causes:

  • Start command failure
  • Missing environment variables
  • Port binding issues (must bind to $PORT)
cf logs my-app --recent

Look for Exited with status 1 or stack trace outputs.

2. Health Check Failures

Apps may fail health checks even if running:

  • Wrong endpoint in http health checks
  • Start delay exceeds timeout in port checks
cf set-health-check my-app port --invocation-timeout 60

For background workers, use none as the health check type.

3. Staging Failures

When pushing apps, staging errors arise due to:

  • Buildpack incompatibility
  • Network access failure (e.g., dependency downloads)
  • Blobstore issues
cf logs my-app --recent

Review Staging failed: Exited with status 137 or OOM errors.

Platform-Level Debugging Techniques

Diego and Cell Logs

Use cf ssh or BOSH CLI to access logs from Diego Cells:

bosh -d cf ssh diego-cell/<index>

Check /var/vcap/sys/log/rep/rep.log and garden/garden.log for container lifecycle events.

Network Routing Issues

Apps might be inaccessible despite being healthy. Possible causes:

  • Route not mapped to app
  • Router not receiving updated route info
  • Firewall blocking traffic to app containers
cf routes
cf map-route my-app example.com --hostname app1

Quota or Resource Exhaustion

Tenant orgs or spaces may hit quotas silently:

cf org-quota org-name
cf space-quota space-name

Resolve by increasing memory, route, or service quotas.

Best Practices for Stability and Observability

Use Structured Logging

Instrument apps to emit JSON logs with request IDs and timestamps. Aggregate with ELK, Splunk, or Datadog to correlate with platform logs.

Properly Configure Health Checks

Misconfigured checks are a top cause of false negatives. Use custom endpoints or increase grace periods where appropriate.

Leverage BOSH for Infrastructure-Level Debugging

BOSH enables SSH access, log inspection, and redeploys for underlying VMs. Use:

bosh -e <env> -d cf instances
bosh logs <job-name>

To track failures at the IaaS level.

Monitor App Resource Utilization

Use the cf app my-app output to monitor memory and CPU usage. Apps frequently restarted for exceeding quotas may benefit from instance scaling or Java tuning.

Handling Persistent Service Failures

Bound Service Unavailability

Failures to bind to services (e.g., Redis, PostgreSQL) often result from misconfigured credentials or expired service plans.

  • Verify credentials in VCAP_SERVICES
  • Check service broker logs via BOSH

Service Broker Failures

When creating or binding fails, run:

cf service my-db

Look for failed states. Check cloud_controller_ng and broker log for root causes.

Conclusion

Troubleshooting Cloud Foundry requires a layered approach—app-level diagnostics, platform services insight, and infrastructure awareness via BOSH. Whether addressing crash loops, routing issues, or service binding errors, effective resolution involves both observability and architectural understanding. Establishing clear logging practices, managing quotas proactively, and building resilient health checks are critical for stable CF deployments in enterprise-scale production systems.

FAQs

1. Why does my app keep restarting in Cloud Foundry?

Common causes include start command errors, port binding failures, or health check misconfiguration. Check cf logs --recent for crash details.

2. How can I debug staging failures?

Use cf logs to view buildpack errors or network issues. Ensure all dependencies are accessible and compatible with the chosen buildpack.

3. What happens if an app exceeds its memory quota?

Cloud Foundry terminates the instance, resulting in crash-restart loops. Tune JVM/memory settings or scale up instance memory.

4. How do I access Diego cell logs?

Use BOSH to SSH into the cell VM and view logs under /var/vcap/sys/log. Look at rep.log and garden.log for container issues.

5. Can I customize health checks per app?

Yes. Use cf set-health-check to define HTTP, port, or none types with timeout configuration specific to the app's startup profile.