WFGY/ProblemMap/GlobalFixMap/OpsDeploy/retry_backoff.md
2025-09-05 11:36:35 +08:00

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Retry and Backoff: OpsDeploy Guardrails

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Make retries safe and predictable. Use structured backoff, deadlines, and idempotent fences so a bad minute does not become a bad day.


Open these first


When to use

  • Provider returns 429 or 5xx or timeouts rise.
  • You integrate a new model provider or gateway.
  • Queue consumers replay after crash or failover.
  • You see retry storms that multiply side effects.

Acceptance targets

  • 429 rate ≤ 0.5 percent at steady state, p95 ≤ 2 percent during bursts.
  • Success after retry ≥ 90 percent for transient classes.
  • Queue wait p95 ≤ 200 ms for read paths, writes use deadlines ≤ 1× p95 service time.
  • ΔS(question, retrieved) and coverage stay inside ship targets while retries occur. λ remains convergent across 2 seeds.

60 second blueprint

  1. Classify errors
    408 429 500 502 503 504 are retriable. 400 401 403 404 are not. 409 is a conflict. Treat as success if idempotency proves the effect already exists.
  2. Set a hard deadline
    Each request carries a client side deadline. Do not exceed it while retrying.
  3. Use full jitter backoff
    Randomized exponential backoff with a cap. Honor Retry After when present.
  4. Coalesce with single flight
    Collapse duplicate work under one in flight key to prevent stampede.
  5. Fence side effects
    Idempotency key on every write and webhook. Exactly once for the effect.

Retry policy matrix

Class Examples Retry? Notes
408 Timeout network idle, upstream slow Yes Backoff with jitter until deadline.
429 Rate limit burst guard Yes Respect Retry After and global token budget.
5xx Transient 500 502 503 504 Yes Retry with jitter. Stop on deadline.
4xx Permanent 400 401 403 404 No Fix request or auth. Do not retry.
409 Conflict idempotency collision No Fetch prior receipt and return.

Backoff recipes

Full jitter exponential

import random, time

def sleep_time(attempt, base=0.25, cap=10.0):
    return random.random() * min(cap, base * (2 ** attempt))

def retry(call, max_attempts=6, deadline_s=20):
    start = time.time()
    for attempt in range(max_attempts):
        ok, res, err, retry_after = call()
        if ok:
            return res
        if time.time() - start >= deadline_s:
            break
        if retry_after:
            time.sleep(min(retry_after, max(0.05, deadline_s - (time.time() - start))))
        else:
            time.sleep(sleep_time(attempt))
    raise RuntimeError("deadline or attempts exhausted")

Decorrelated jitter

import random

def deco_jitter(prev, base=0.25, cap=10.0):
    return min(cap, random.uniform(base, prev * 3 or base))

Choose one strategy and stick to it across clients and workers.


Queue consumers and jobs

  • Acknowledge only after the effect is sealed. See idempotency_dedupe.md.
  • Use per message deadlines and per topic concurrency caps.
  • Backoff queues on provider 429 or store saturation.
  • Include idempotency_key, attempt, and first_seen_at in logs.

HTTP client rules

  • Honor Retry After in seconds or HTTP date.
  • Propagate X Request Id and a stable Idempotency Key for writes.
  • Set Request Deadline header for end to end visibility.
  • Stop retries on 4xx except 408. Stop after deadline or attempts.

Single flight pattern

Coalesce identical misses so one worker computes the result.

key = f"wf:{hash(request_body)}"
if redis.set(f"lock:{key}", "1", nx=True, px=30000):
    try:
        val = compute()
        redis.set(f"ans:{key}", serialize(val), ex=60)
    finally:
        redis.delete(f"lock:{key}")
else:
    val = wait_poll(f"ans:{key}", timeout_ms=1500)
return val

YAML policy you can paste

# opsdeploy/retry_backoff.yml
retry:
  strategy: full_jitter
  base_s: 0.25
  cap_s: 10
  max_attempts: 6
  honor_retry_after: true
deadlines:
  read_ms: 2000
  write_ms: 3000
class_rules:
  retriable:   [408, 429, 500, 502, 503, 504]
  nonretry:    [400, 401, 403, 404]
  conflict_ok: [409]
single_flight:
  enabled: true
  lease_ms: 30000
observability:
  log_fields:
    - request_id
    - idempotency_key
    - attempt
    - retry_after
    - sleep_ms
    - deadline_ms
decision:
  abort_when:
    timeout_rate_p95: ">=0.02"
    ds_p95_drift: ">=0.15"
    error_rate: ">=0.01"

Observability you must log

  • Attempts, sleep times, adherence to Retry After.
  • Deadline budget spent and remaining at each hop.
  • 429 and 5xx counts by endpoint and tenant.
  • Success after retry ratio and time to success.
  • Quality under pressure, ΔS and coverage, λ states.

Symptom to fix map

Symptom Likely cause Open this
Retry storms after deploy no jitter, no global cap rate_limit_backpressure.md
Double writes on retry missing idempotency fences idempotency_dedupe.md
Mixed answers across versions cache keys not partitioned by pins cache_warmup_invalidation.md
First call fails after cutover boot order or index pointer wrong bootstrap-ordering.md, vector_index_build_and_swap.md
Tail latency explodes unbounded concurrency or no deadlines rate_limit_backpressure.md

Common pitfalls

  • Retrying nonretriable 4xx and burning budget.
  • Ignoring Retry After and syncing retries across clients.
  • No deadline at the client so retries outlive the user.
  • No idempotency for writes so duplicates slip in.
  • Retries that cross a blue green boundary without version pins.

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