Bindu - A2A Protocol Compliant AI Agent Framework

Things fail in production for ordinary reasons. A database connection drops. Redis goes away for a moment. An API times out. Most of those failures are transient. If the system treats every one of them as final, tasks fail for no good reason and recovering services get hammered the instant they come back. Bindu wraps every brittle boundary — workers, storage, scheduler, outbound HTTP — in a small set of Tenacity decorators that retry transient errors with exponential backoff and reraise everything else immediately.

Why Retry Matters

Without retry	With Bindu retry
Temporary failures surface as immediate task failures	Transient errors recover automatically before users see them
Recovering services get a thundering herd	Per-attempt backoff (with jitter on three of four families) spreads load
Worker, storage, scheduler, and HTTP each need custom handling	Four named decorators wrap the same Tenacity machinery
Logic bugs and transient errors are retried indistinguishably	Only a narrow allowlist of transient exceptions is retried
Tuning behaviour requires code changes	`RETRY__*` env vars override every default

How Bindu Retry Works

All four decorators are thin wrappers around a single factory, create_retry_decorator(operation_type, ...), defined in bindu/utils/retry.py. The factory:

Looks up the family’s defaults on app_settings.retry (or honours your override).
Picks a wait strategy — wait_random_exponential (jitter) or wait_exponential (no jitter).
Builds an AsyncRetrying loop that retries only on TRANSIENT_EXCEPTIONS.
Logs at WARNING before each sleep (via before_sleep_log) and at INFO after each attempt (via after_log).
Reraises the original exception once attempts are exhausted (reraise=True).

Only transient exceptions are retried. Application errors like ValueError or KeyError raise on the first attempt — they are not in the retry list.

The Lifecycle: Fail, Wait, Try Again

What Counts As Transient

The allowlist lives in bindu/utils/retry.py as TRANSIENT_EXCEPTIONS:

TRANSIENT_EXCEPTIONS = (
    ConnectionError,
    ConnectionRefusedError,
    ConnectionResetError,
    ConnectionAbortedError,
    TimeoutError,
    asyncio.TimeoutError,
    OSError,  # covers BrokenPipeError and friends
)

A second tuple, HTTP_RETRYABLE_EXCEPTIONS, extends this with HTTPConnectionError, HTTPTimeoutError, and HTTPServerError (5xx). It is defined for HTTP callers but the four headline decorators currently all use TRANSIENT_EXCEPTIONS.

Subclasses count: any custom exception that inherits from ConnectionError, TimeoutError, or OSError is retried automatically.

Backoff: Plain vs. Jittered

Bindu picks between two Tenacity wait strategies per family:

wait_strategy = (
    wait_random_exponential(multiplier=1, min=_min_wait, max=_max_wait)
    if use_jitter
    else wait_exponential(multiplier=1, min=_min_wait, max=_max_wait)
)

wait_exponential doubles the wait each attempt, clamped to [min_wait, max_wait]. Deterministic. Used for storage.
wait_random_exponential samples uniformly in [0, min(max_wait, multiplier * 2^attempt)]. Spreads retries to avoid thundering herds. Used for worker, scheduler, and api.

Storage is intentionally jitter-free: a single process serialises its own retries, and deterministic backoff is easier to reason about against a local in-memory store. Anything that talks over the network gets jitter so that N pods don’t all retry at the same instant.

The Four Decorator Families

retry_worker_operation

Wraps ManifestWorker task execution. Default 3 attempts, 1.0–10.0 s, jittered. Used in bindu/server/workers/manifest_worker.py on run_task and cancel_task.

retry_storage_operation

Wraps storage CRUD on the in-memory backend. Default 5 attempts, 0.5–5.0 s, no jitter. Used in bindu/server/storage/memory_storage.py on load_task, submit_task, update_task.

retry_scheduler_operation

Wraps scheduler enqueue calls. Default 3 attempts, 1.0–8.0 s, jittered. Used in bindu/server/scheduler/memory_scheduler.py and bindu/server/scheduler/redis_scheduler.py on run_task, cancel_task, pause_task, resume_task.

retry_api_call

Wraps outbound HTTP. Default 4 attempts, 1.0–15.0 s, jittered. Used via create_retry_decorator("api") on the HTTP client in bindu/utils/http/client.py (get, post, put, delete, request) and on push delivery in bindu/utils/notifications.py (_post_with_retry).

All four call into the same create_retry_decorator(operation_type, ...) factory. They exist as named convenience wrappers for grep-ability and for backward compatibility — calling create_retry_decorator("api") is exactly equivalent to retry_api_call().

Why four decorators, not one?

The split is operational, not technical:

Storage retries should be many and fast — a flaky local connection deserves five 0.5–5 s pokes, not three 10 s sulks. Storage runs in-process, so jitter buys you nothing.
API retries should be fewer and longer — remote services need room to breathe, and jitter prevents pods from synchronising.
Worker retries cover task execution and should be conservative; retrying agent logic too aggressively masks real bugs.
Scheduler retries cover broker hand-off, where the failure mode is “Redis briefly unavailable” — short attempts, modest wait.

Each family has its own env knobs so you can tune them independently without rebuilding the image.

Defaults and Configuration

Family Defaults

Defined in RetrySettings (bindu/settings.py):

Family	`max_attempts`	`min_wait`	`max_wait`	Jitter
worker	3	1.0 s	10.0 s	yes
storage	5	0.5 s	5.0 s	no
scheduler	3	1.0 s	8.0 s	yes
api	4	1.0 s	15.0 s	yes

Environment Variables

RetrySettings lives under the top-level Settings model, which uses env_nested_delimiter="__". The variable name is RETRY__<field>:

# Worker
RETRY__WORKER_MAX_ATTEMPTS=3
RETRY__WORKER_MIN_WAIT=1.0
RETRY__WORKER_MAX_WAIT=10.0

# Storage
RETRY__STORAGE_MAX_ATTEMPTS=5
RETRY__STORAGE_MIN_WAIT=0.5
RETRY__STORAGE_MAX_WAIT=5.0

# Scheduler
RETRY__SCHEDULER_MAX_ATTEMPTS=3
RETRY__SCHEDULER_MIN_WAIT=1.0
RETRY__SCHEDULER_MAX_WAIT=8.0

# External API
RETRY__API_MAX_ATTEMPTS=4
RETRY__API_MIN_WAIT=1.0
RETRY__API_MAX_WAIT=15.0

Per-call overrides on the decorator (@retry_storage_operation(max_attempts=10)) win over env vars, which win over the defaults baked into RetrySettings. The or fallback inside create_retry_decorator means an override of 0 or None falls back to settings — pass a real positive value.

Decorator Reference

retry_worker_operation()

Family: worker · Jitter: yes · Defaults: 3 attempts, 1.0–10.0 sWraps task execution on ManifestWorker. Failures during manifest.run(...) only retry when they bubble up as ConnectionError/TimeoutError/OSError. Agent-side ValueError or RuntimeError is not retried — the worker catches it, marks the task failed, and reraises.Real call sites (bindu/server/workers/manifest_worker.py):

@retry_worker_operation()                     # line 96
async def run_task(self, params: TaskSendParams) -> None: ...

@retry_worker_operation(max_attempts=2)       # line 232
async def cancel_task(self, params: TaskIdParams) -> None: ...

cancel_task deliberately caps at 2 attempts: a cancel that fails twice is not going to start working on attempt three.

retry_storage_operation()

Family: storage · Jitter: no (wait_exponential) · Defaults: 5 attempts, 0.5–5.0 sWraps storage CRUD on InMemoryStorage. The implementation overrides per-call to a tighter budget tuned for in-process memory:bindu/server/storage/memory_storage.py (lines 41–44):

DEFAULT_STORAGE_RETRY_ATTEMPTS = 3
DEFAULT_STORAGE_MIN_WAIT = 0.1
DEFAULT_STORAGE_MAX_WAIT = 1.0

Applied at lines 71, 103, 242:

@retry_storage_operation(
    max_attempts=DEFAULT_STORAGE_RETRY_ATTEMPTS,
    min_wait=DEFAULT_STORAGE_MIN_WAIT,
    max_wait=DEFAULT_STORAGE_MAX_WAIT,
)
async def load_task(self, task_id, history_length=None) -> Task | None: ...

Same decorator covers submit_task and update_task.

The Postgres storage backend does not use @retry_storage_operation. It calls execute_with_retry directly via its own _retry_on_connection_error helper (bindu/server/storage/postgres_storage.py line 243), keyed off storage.postgres_max_retries and storage.postgres_retry_delay from StorageSettings. So the RETRY__STORAGE_* env vars affect the in-memory backend and any code that uses the decorator directly — they do not retune Postgres.

retry_scheduler_operation()

Family: scheduler · Jitter: yes · Defaults: 3 attempts, 1.0–8.0 sWraps the four enqueue operations on both scheduler backends.bindu/server/scheduler/redis_scheduler.py (lines 114, 124, 134, 144):

@retry_scheduler_operation()
async def run_task(self, params: TaskSendParams) -> None: ...

@retry_scheduler_operation()
async def cancel_task(self, params: TaskIdParams) -> None: ...

@retry_scheduler_operation()
async def pause_task(self, params: TaskIdParams) -> None: ...

@retry_scheduler_operation()
async def resume_task(self, params: TaskIdParams) -> None: ...

bindu/server/scheduler/memory_scheduler.py (lines 73, 83, 93, 103) overrides defaults for its anyio stream — tight 0.1–1.0 s window across 3 attempts:

DEFAULT_RETRY_ATTEMPTS = 3
DEFAULT_RETRY_MIN_WAIT = 0.1
DEFAULT_RETRY_MAX_WAIT = 1.0

@retry_scheduler_operation(
    max_attempts=DEFAULT_RETRY_ATTEMPTS,
    min_wait=DEFAULT_RETRY_MIN_WAIT,
    max_wait=DEFAULT_RETRY_MAX_WAIT,
)
async def run_task(self, params: TaskSendParams) -> None: ...

retry_api_call()

Family: api · Jitter: yes · Defaults: 4 attempts, 1.0–15.0 sThe headline name. Internally, Bindu’s HTTP client and push notifier reach for the factory directly so they can mix in extra parameters.bindu/utils/http/client.py (lines 195, 219, 245, 271, 291):

@create_retry_decorator("api")
async def get(self, endpoint, *, params=None, headers=None, **kwargs): ...

@create_retry_decorator("api")
async def post(self, endpoint, *, data=None, json=None, headers=None, **kwargs): ...

bindu/utils/notifications.py (line 125) — push delivery uses a tighter override:

@create_retry_decorator("api", max_attempts=3, min_wait=0.5, max_wait=5.0)
async def _post_with_retry(self, url, resolved_ip, headers, payload, event): ...

Push delivery additionally short-circuits the retry for 4xx (except 429) inside the wrapped body — the decorator only sees the exceptions you let escape.

Inside an Attempt

Invoke the wrapped function

AsyncRetrying enters its loop with stop=stop_after_attempt(N), wait=<exponential strategy>, retry=retry_if_exception_type(TRANSIENT_EXCEPTIONS), reraise=True. A debug log records the attempt number.

On success: stop

The with attempt: block records success; the async for exits and the wrapper returns the value.

On non-transient exception: reraise now

Anything outside TRANSIENT_EXCEPTIONS (e.g. ValueError) skips the retry-decision path and propagates immediately. There is no backoff and no further attempt.

On transient exception: log and sleep

before_sleep_log(logger, WARNING) writes a warning. The wait strategy computes the next sleep — min(max_wait, multiplier * 2^attempt) either deterministic (storage) or sampled uniformly (everyone else). after_log(logger, INFO) records the attempt outcome.

On exhaustion: reraise the last exception

Once stop_after_attempt trips, reraise=True means the original exception is raised — not a RetryError. Callers see the underlying ConnectionError and can catch it normally.

Examples

Custom decorator usage

from bindu.utils.retry import (
    retry_worker_operation,
    retry_storage_operation,
    retry_api_call,
)

@retry_worker_operation(max_attempts=2)
async def cancel_task(self, params): ...

@retry_storage_operation(max_attempts=10, min_wait=2.0)
async def slow_update(self, task_id, state): ...

@retry_api_call(max_attempts=6, max_wait=30.0)
async def call_llm(self, prompt: str) -> str: ...

Ad-hoc retry (no decorator)

execute_with_retry is what applications.py uses to retry storage and scheduler construction at startup, and what postgres_storage.py uses for every query.

from bindu.utils.retry import execute_with_retry

result = await execute_with_retry(
    fetch_remote_thing,
    "task_id_123",
    max_attempts=5,
    min_wait=1.0,
    max_wait=10.0,
)

It uses wait_random_exponential (jitter) and the same TRANSIENT_EXCEPTIONS allowlist.

Env-var overrides for a noisy network

# Network-flaky environment: more attempts, longer ceiling
RETRY__API_MAX_ATTEMPTS=6
RETRY__API_MIN_WAIT=2.0
RETRY__API_MAX_WAIT=30.0

# Local dev with reliable storage: keep retries snappy
RETRY__STORAGE_MAX_ATTEMPTS=3
RETRY__STORAGE_MIN_WAIT=0.1
RETRY__STORAGE_MAX_WAIT=1.0

Make sure operations are idempotent

Anything wrapped by a retry decorator should be safe to run twice. Set-like operations are naturally idempotent:

@retry_storage_operation()
async def update_task_status(self, task_id: UUID, status: str) -> None:
    await self.db.execute(
        "UPDATE tasks SET status = :status WHERE task_id = :task_id",
        {"status": status, "task_id": task_id},
    )

Distinguish transient from logic errors

@retry_api_call()
async def call_api(self, data: dict) -> dict:
    response = await api_client.post("/endpoint", json=data)
    if response.status_code == 400:
        raise ValueError("Invalid request")  # NOT retried - not in TRANSIENT_EXCEPTIONS
    if response.status_code >= 500:
        raise ConnectionError("Upstream 5xx")  # retried
    return response.json()

Sample log output

A storage call that fails twice then succeeds (logger bindu.utils.retry):

[DEBUG] bindu.utils.retry  Executing storage operation load_task (attempt 1/5)
[WARNING] bindu.utils.retry  Retrying ... in 0.5 seconds as it raised ConnectionError: Database connection lost.
[INFO] bindu.utils.retry   Finished call to 'load_task' after 0.512(s), this was the 1 time calling it.
[DEBUG] bindu.utils.retry  Executing storage operation load_task (attempt 2/5)
[WARNING] bindu.utils.retry  Retrying ... in 1.0 seconds as it raised ConnectionError: Database connection lost.
[INFO] bindu.utils.retry   Finished call to 'load_task' after 1.013(s), this was the 2 time calling it.
[DEBUG] bindu.utils.retry  Executing storage operation load_task (attempt 3/5)
[INFO] bindu.utils.retry   Finished call to 'load_task' after 0.004(s), this was the 3 time calling it.

The before_sleep_log / after_log lines come from Tenacity directly; the Executing ... operation line comes from the wrapper inside create_retry_decorator.

Troubleshooting

Retries are taking too long. Lower max_attempts and/or max_wait:

RETRY__WORKER_MAX_ATTEMPTS=2
RETRY__WORKER_MAX_WAIT=5.0

An operation never retries. The exception is not in TRANSIENT_EXCEPTIONS. Either subclass ConnectionError/TimeoutError/OSError in your own exception, or wrap it before raising:

try:
    await flaky_call()
except SomeLibraryError as e:
    raise ConnectionError(str(e)) from e

Retries hide a real bug. A logic error wrapped as ConnectionError will be retried N times before failing — exactly what you don’t want. Keep TRANSIENT_EXCEPTIONS narrow and raise application errors as ValueError/RuntimeError so they fail fast. Postgres retries don’t respond to RETRY__STORAGE_*. Correct — Postgres uses storage.postgres_max_retries / storage.postgres_retry_delay from StorageSettings, not RetrySettings.

Testing

import pytest
from bindu.utils.retry import retry_worker_operation

@pytest.mark.asyncio
async def test_retry_success_after_failure():
    attempts = 0

    @retry_worker_operation(max_attempts=3, min_wait=0.01, max_wait=0.05)
    async def flaky():
        nonlocal attempts
        attempts += 1
        if attempts < 3:
            raise ConnectionError("transient")
        return "ok"

    assert await flaky() == "ok"
    assert attempts == 3

uv run pytest tests/unit/test_retry.py -v

Storage — backend that exposes the in-memory @retry_storage_operation calls and the Postgres _retry_on_connection_error helper.
Scheduler — Redis and in-memory schedulers whose enqueue paths are retry-wrapped.
Notifications — push delivery uses @create_retry_decorator("api", ...) with its own tighter budget.
Observability — every retry attempt is logged via the bindu.utils.retry logger and surfaced through your existing log pipeline.

Bindu treats transient failures assomething to recover from, not something to fearso agents stay resilient when networks, databases, and APIs stumble.

Developer Journey

Retry Mechanism

Why Retry Matters

How Bindu Retry Works

The Lifecycle: Fail, Wait, Try Again

What Counts As Transient

Backoff: Plain vs. Jittered

The Four Decorator Families

retry_worker_operation

retry_storage_operation

retry_scheduler_operation

retry_api_call

Why four decorators, not one?

Defaults and Configuration

Family Defaults

Environment Variables

Decorator Reference

Inside an Attempt

Examples

Custom decorator usage

Ad-hoc retry (no decorator)

Env-var overrides for a noisy network

Make sure operations are idempotent

Distinguish transient from logic errors

Sample log output

Troubleshooting

Testing

​Why Retry Matters

​How Bindu Retry Works

​The Lifecycle: Fail, Wait, Try Again

​What Counts As Transient

​Backoff: Plain vs. Jittered

​The Four Decorator Families

retry_worker_operation

retry_storage_operation

retry_scheduler_operation

retry_api_call

​Why four decorators, not one?

​Defaults and Configuration

​Family Defaults

​Environment Variables

​Decorator Reference

​Inside an Attempt

​Examples

​Custom decorator usage

​Ad-hoc retry (no decorator)

​Env-var overrides for a noisy network

​Make sure operations are idempotent

​Distinguish transient from logic errors

​Sample log output

​Troubleshooting

​Testing

​Related

Why Retry Matters

How Bindu Retry Works

The Lifecycle: Fail, Wait, Try Again

What Counts As Transient

Backoff: Plain vs. Jittered

The Four Decorator Families

Why four decorators, not one?

Defaults and Configuration

Family Defaults

Environment Variables

Decorator Reference

Inside an Attempt

Examples

Custom decorator usage

Ad-hoc retry (no decorator)

Env-var overrides for a noisy network

Make sure operations are idempotent

Distinguish transient from logic errors

Sample log output

Troubleshooting

Testing

Related