Best Monitoring Tools for Internal APIs

The Internal API Monitoring Challenge

Internal APIs power your application:

• Service-to-service communication
• Backend for frontend (BFF) layers
• Database APIs and caching layers
• Authentication and authorization services
• Message queue consumers

When they fail, your application fails. But monitoring them isn't straightforward:

• Not publicly accessible: Firewalls block external requests
• No DNS: Often accessed by internal hostnames or IPs
• Network complexity: VPCs, VPNs, private subnets
• Authentication: Internal auth mechanisms

Monitoring Approaches

1. Private/Internal Probes

Run monitoring probes inside your network.

How it works:

• Deploy a probe agent inside your infrastructure
• Agent performs checks and reports to central monitoring
• Can reach any internal endpoint

Best for: Teams using cloud monitoring who need internal visibility

Tools that support this:

• Datadog (Private Locations)
• Checkly (Private Locations)
• Grafana Synthetic Monitoring (Private Probes)
• Wakestack (Agent-based)

2. Agent-Based Monitoring

Install agents that report health from within.

How it works:

• Agent runs on each server/container
• Reports metrics including API health
• No inbound connections required

Best for: Teams who want combined infrastructure + API monitoring

Tools:

• Wakestack
• Datadog
• New Relic
• Prometheus (with push gateway)

3. Sidecar/Service Mesh Monitoring

Monitor at the network layer.

How it works:

• Service mesh (Istio, Linkerd) intercepts traffic
• Automatically collects latency, errors, throughput
• No application changes needed

Best for: Kubernetes environments with service mesh

Tools:

• Istio + Prometheus
• Linkerd + Grafana
• Consul Connect

4. Application-Level Health Checks

Build monitoring into your services.

How it works:

• Services expose /health endpoints
• Internal monitoring polls these endpoints
• Health checks verify dependencies

Best for: Any environment, especially microservices

Implementation: Custom code + any internal monitoring tool

5. Self-Hosted Monitoring

Run your own monitoring stack internally.

How it works:

• Deploy Prometheus/Grafana inside your network
• Scrape internal API metrics
• Full control, no external dependencies

Best for: Teams wanting complete control

Tools:

• Prometheus + Grafana
• Netdata
• Zabbix

Best Tools for Internal API Monitoring

1. Prometheus + Blackbox Exporter

Best for: Self-hosted internal API probing

The blackbox exporter probes endpoints over HTTP, TCP, ICMP, or DNS from inside your network.

Setup:

# prometheus.yml
scrape_configs:
  - job_name: 'internal-apis'
    metrics_path: /probe
    params:
      module: [http_2xx]
    static_configs:
      - targets:
        - http://user-service:8080/health
        - http://order-service:8080/health
        - http://payment-service:8080/health
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - target_label: __address__
        replacement: blackbox-exporter:9115

What you get:

• Probe success/failure
• Response time
• SSL certificate info
• DNS resolution time

Cost: Free

2. Wakestack

Best for: Simple internal monitoring with cloud convenience

Wakestack's agent runs inside your network and can monitor internal endpoints while reporting to the cloud dashboard.

Why it works:

• Agent installed on your servers
• Monitors internal services
• Cloud dashboard for visibility
• No inbound firewall rules needed

What you get:

• Internal HTTP checks
• Server metrics
• Unified view of internal + external
• Alerting

Cost: Based on hosts

3. Checkly Private Locations

Best for: Teams already using Checkly who need internal monitoring

Checkly lets you deploy private probe locations inside your network.

Setup:

• Deploy Checkly agent in your VPC
• Configure checks to use private location
• Same dashboard as public checks

What you get:

• Full Checkly check types internally
• Unified monitoring view
• Monitoring as code support

Cost: Requires Checkly paid plan

4. Datadog Private Locations

Best for: Enterprise teams using Datadog

Datadog Synthetic Monitoring supports private locations for internal API testing.

Setup:

• Deploy Datadog private location worker
• Create synthetic tests targeting internal URLs
• Results appear in Datadog dashboard

What you get:

• Full synthetic monitoring internally
• API tests with assertions
• Multi-step transactions
• Integration with Datadog ecosystem

Cost: Requires Datadog Synthetic Monitoring

5. Grafana Synthetic Monitoring

Best for: Teams using Grafana Cloud

Grafana's synthetic monitoring supports private probes.

Setup:

• Deploy private probe agent
• Configure checks in Grafana Cloud
• View alongside other metrics

What you get:

• HTTP, DNS, TCP checks
• Integration with Grafana dashboards
• Alerting

Cost: Included in Grafana Cloud

Implementation Patterns

Health Endpoint Standard

Every internal API should expose a health endpoint:

GET /health

Response:
{
  "status": "healthy",
  "checks": {
    "database": "ok",
    "cache": "ok",
    "dependency-service": "ok"
  }
}

Monitor this endpoint to catch failures quickly.

Dependency Checks

Internal APIs often depend on other services. Health checks should verify dependencies:

User Service → Database ✓
User Service → Auth Service ✓
User Service → Cache ✓
Overall: Healthy

If a dependency is down, the health check should reflect it.

Liveness vs Readiness

Liveness: Is the process running?

• Simple check
• If failing, restart the service

Readiness: Can it handle requests?

• Checks dependencies
• If failing, remove from load balancer

Monitor both for complete visibility.

Circuit Breaker Metrics

If you use circuit breakers, monitor their state:

• Closed: Normal operation
• Open: Calls are failing, circuit tripped
• Half-Open: Testing if service recovered

Circuit breaker state changes indicate problems.

Comparison Table

Best Practices

Monitor What Matters

Not every internal endpoint needs monitoring. Prioritize:

1. Critical paths: Auth, payments, core business logic
2. Single points of failure: Databases, caches
3. High-traffic services: Services that handle most requests
4. Dependencies: External services you rely on

Set Appropriate Thresholds

Internal APIs often have different SLOs than public APIs:

• Latency: Internal calls should be faster (no internet)
• Availability: May need higher uptime (cascading failures)
• Error rates: Lower tolerance (internal issues = bugs)

Alert on Trends, Not Blips

A single failed health check isn't necessarily a problem:

• Network hiccup
• GC pause
• Deployment in progress

Alert on sustained failures (2-3 consecutive) or degradation trends.

Include in Deploy Pipelines

Check internal API health as part of deployment:

1. Deploy new version
2. Wait for health check to pass
3. If healthy, proceed with rollout
4. If unhealthy, rollback

Summary

Monitoring internal APIs requires different approaches than public APIs:

Best tools:

• Prometheus + Blackbox Exporter: Self-hosted, flexible
• Wakestack: Agent-based, simple
• Checkly/Datadog/Grafana: Cloud with private probes

Key approaches:

• Private probe nodes inside your network
• Agent-based monitoring that reports out
• Self-hosted monitoring infrastructure
• Application health endpoints

Best practices:

• Every service exposes /health
• Check dependencies in health checks
• Monitor critical paths first
• Alert on sustained failures, not blips

Internal APIs are the backbone of your application. They deserve the same monitoring attention as your public interfaces—often more.