microburst

AWS failure injection that your SDK actually believes.
Throttling, latency, timeouts and resets — in the exact wire format AWS uses,
so retry, backoff and circuit-breaker code gets exercised for real.

The problem

Your app handles ThrottlingException and retries with backoff — or so you hope. The only way to know is to make AWS actually throttle you, and until now your options were:

microburst is the missing piece: a standalone, protocol-aware proxy that works against any AWS-compatible endpoint — MiniStack, moto, or real AWS — and returns failures the SDK can't tell apart from the real thing.

Why "protocol-aware" matters

SDKs decide whether to retry by parsing the error code out of the response body, and whether that code is retryable depends on the status too. S3 SlowDown at HTTP 400 is a terminal client error; at 503 the SDK backs off and retries. Get the shape wrong and you're testing a failure AWS never produces.

microburst reads the botocore service models — the same definitions the SDK uses — so injected errors carry the right code, the right XML/JSON envelope, and the right status.

Install

pip install microburst        # or: uvx microburst

Quickstart

microburst --upstream http://localhost:4566   # your emulator, e.g. MiniStack

export AWS_ENDPOINT_URL=http://localhost:9999
python your_app.py        # all AWS calls now flow through microburst

Inject throttling at runtime:

curl -X PATCH localhost:9999/_microburst/rules -d '[
  {"service": "dynamodb", "probability": 0.3,
   "error": {"code": "ProvisionedThroughputExceededException"}}
]'

Or fire a preset:

curl -X POST localhost:9999/_microburst/presets/ddb-throttle

Then watch exactly what fired — chaos you can audit:

curl localhost:9999/_microburst/fired
# → [{"rule": "...", "service": "dynamodb", "operation": "PutItem",
#     "action": "error:ProvisionedThroughputExceededException", ...}]

Rules

- service: dynamodb          # SigV4 credential-scope name, "*" for all
  operation: PutItem         # optional; resolved per AWS protocol
  region: us-east-1          # optional
  resource: orders           # substring of table/bucket/queue/…
  headers:                   # optional; all must match (substring)
    x-amz-acl: public-read   # e.g. only canned-ACL puts
    x-amz-copy-source: ""    # "" = presence check (e.g. CopyObject)
  body: "TableName == 'orders'"        # jmespath on JSON/form body — truthy = match
  rate: {count: 5, window_s: 60}       # at most N fires per rolling window
  sequence: {fail: 3, pass: 2}         # fail 3, pass 2, repeat
  probability: 0.5           # default 1.0
  deterministic: true        # hash the request identity — the same resource
                             # always lands on the same side of p (reproducible
                             # "this bucket always fails" without RNG seeds)
  times: 3                   # fire at most N times, then pass through
  ttl_s: 120                 # rule expires N seconds after creation
  error:
    code: SlowDown           # omit → samples a plausible modeled exception
    status: 503              # omit → modeled/curated AWS status
    message: "slow down"
  latency: {min: 500, max: 2000}   # ms; or a bare number, or a distribution:
                                   # {dist: gaussian, mean: 500, stddev: 100,
                                   #  min: 100, max: 2000}
                                   # {dist: spike, min: 50, max: 100,
                                   #  spike_ms: 5000, spike_p: 0.05}
  timeout_ms: 30000                # hold the connection, then 504
  reset: true                      # abort the TCP connection
  response:                        # post-forward: mutate the upstream response
    truncate_frac: 0.5             # valid envelope, body cut short (or
                                   # truncate_bytes: N)
    abort_frac: 0.3                # send 30%, then kill the connection
                                   # mid-stream (or abort_bytes: N)
    corrupt_bytes: 16              # flip N bytes — 200 OK, wrong payload
    bandwidth_kbps: 64             # cap downstream throughput

times: 1 is the sleeper feature — "fail exactly once, then let the retry succeed" verifies your retry path end-to-end instead of just proving errors surface.

Presets

ddb-throttle · flaky-s3 · slow-lambda · kms-outage · sqs-backlog · regional-failover · network-jitter · gateway-storm

Control API

Load rules at startup with microburst --config chaos.yml (see examples/chaos.yml).

Real AWS upstreams

microburst --upstream https://dynamodb.us-east-1.amazonaws.com

Requests are re-signed with your credentials automatically for amazonaws.com upstreams (--no-resign to disable). Useful for game days against staging accounts.

Caveats

• HTTP/1.1 data plane; event-stream APIs pass through but per-frame fault injection isn't implemented yet.
• Bodies > 4 MiB are streamed uninspected (resource matchers won't apply; service/operation still do for REST services).
• The control API is unauthenticated — bind it to localhost only.
• SigV4A (multi-region) requests parse fine; rules see region: "*".

Demo

With MiniStack (or any emulator) on :4566:

python demo.py   # orders pipeline → microburst → MiniStack, scripted fault windows

You'll see DynamoDB puts retry through injected throttling, SQS publishes degrade under latency, S3 reads ride out SlowDown, and the pipeline recover when faults clear — plus the fired-fault ledger at the end.

Contributing & community

• Contributing · Code of Conduct · Security
• This repo adopts Apache Magpie for agent-assisted maintainership (see .apache-magpie.lock).

License

MIT — go break your own stuff before production does.