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FAQ: Checking Node Probability and Status

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How to use the M-Lab Locate Service API to verify your node's probability setting and registration status.

beginner Node Operations

Q: How can I verify my node’s current probability setting and registration status?

A: Use the M-Lab Locate Service API to check whether your node is registered, its current probability, and which experiments it’s serving.

Query the Locate API

curl "https://locate.measurementlab.net/v2/nearest/ndt/ndt7" | jq .

If your node is registered and healthy, it will appear in the results array. The response includes the FQDN, access URLs, and any active experiments.

Check Node Probability

Each node has a probability value (0.0–1.0) that controls how often the Locate API directs clients to it. A probability of 1.0 means the node is fully active; 0.0 means it’s disabled.

You can query a specific node:

curl "https://locate.measurementlab.net/v2/nearest/ndt/ndt7?lat=<LAT>&lon=<LON>" | jq '.results[] | select(.machine | contains("your-node-hostname"))'

Common Registration Issues

  • Node not appearing — check that the register-node container is running and healthy: 
    docker compose ps register-node
docker compose logs register-node --tail 50
  • Probability unexpectedly 0 — M-Lab may have flagged your node for a health check failure; check the host-service metrics endpoint
  • Stale registration — if you recently changed your node’s IP or hostname, it may take up to 10 minutes for the Locate API to reflect the update

Prometheus Metrics

Your node exposes health metrics at http://your-node:9990/metrics. Key metrics to check:

ndt_e2e_latency_seconds    — end-to-end test latency
ndt_client_connections     — number of active client connections
registration_last_success  — timestamp of last successful registration