Reliability Controls¶

This guide provides command-first setup for request protection and failure handling: concurrency limits, retries, and circuit breakers.

1. Concurrency and Queue Limits¶

Cap how many requests the gateway runs at once, and how many can wait:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 \
  --max-concurrent-requests 100 \
  --queue-size 200 \
  --queue-timeout-secs 30

Each admitted request holds a permit until its response finishes, streaming included, so at most 100 requests are in flight.
Up to 200 more wait in arrival order. A request that finds the queue full gets 429; one that waits longer than 30 seconds gets 503. Both carry Retry-After: 2.
Size --max-concurrent-requests from what your workers can run at once; see Sizing Guidelines.

Leave --rate-limit-tokens-per-second unset. A positive rate also refills the bucket over time, so requests in flight can exceed the cap. Set it only to keep the pre-v1.10 burst-rate behavior:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 \
  --max-concurrent-requests 100 \
  --rate-limit-tokens-per-second 100 \
  --queue-size 200 \
  --queue-timeout-secs 30

For per-worker load thresholds that take a saturated worker out of routing, see Overload Protection.

2. Retries¶

Enable retries with explicit backoff settings:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 \
  --retry-max-retries 5 \
  --retry-initial-backoff-ms 50 \
  --retry-max-backoff-ms 30000 \
  --retry-backoff-multiplier 1.5 \
  --retry-jitter-factor 0.2

Disable retries when client handles them:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 \
  --disable-retries

3. Circuit Breakers¶

Protect traffic from repeatedly failing workers:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 \
  --cb-failure-threshold 10 \
  --cb-success-threshold 3 \
  --cb-timeout-duration-secs 60

A worker's circuit opens after 10 consecutive failures (408, 500, 502, 503, 504, or no response). A 429 from a worker is capacity pushback: it can still be retried, but it never opens or closes the circuit. See What Counts as a Failure. --cb-window-duration-secs is accepted but not used by the breaker.

Disable only for controlled testing:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 \
  --disable-circuit-breaker

Production Baseline¶

A practical starting profile:

smg launch \
  --worker-urls http://w1:8000 http://w2:8000 http://w3:8000 \
  --max-concurrent-requests 150 \
  --queue-size 300 \
  --queue-timeout-secs 30 \
  --retry-max-retries 3 \
  --retry-initial-backoff-ms 50 \
  --retry-max-backoff-ms 5000 \
  --retry-backoff-multiplier 2.0 \
  --retry-jitter-factor 0.2 \
  --cb-failure-threshold 10 \
  --cb-success-threshold 3 \
  --cb-timeout-duration-secs 60

Verify¶

curl http://localhost:30000/health
curl http://localhost:30000/workers

# Admission and circuit breaker metrics (Prometheus port, default 29000)
curl -s http://localhost:29000/metrics | grep -E '^smg_(admission|http_rate_limit|worker_cb)'

Admission metrics appear once requests start going through admission control.