feat: add startup retry with exponential backoff for Redis connection (#20)

README.md

@@ -56,6 +56,7 @@ except DuplicateTaskError:
 - **Explicit lock key** — pin any task to a fixed Redis key with `deduplication_key`, bypassing fingerprint computation entirely.
 - **Partial fingerprint** — deduplicate on a subset of kwargs with `deduplication_key_fields`, ignoring irrelevant arguments.
 - **Per-task opt-out** — disable deduplication for individual tasks with the `deduplication` label.
+- **Startup resilience** — automatic reconnection with exponential backoff if Redis is unavailable at broker startup.
 
 ## License
 

docs/index.md

@@ -56,6 +56,7 @@ except DuplicateTaskError:
 - **Explicit lock key** — pin any task to a fixed Redis key with `deduplication_key`, bypassing fingerprint computation entirely.
 - **Partial fingerprint** — deduplicate on a subset of kwargs with `deduplication_key_fields`, ignoring irrelevant arguments.
 - **Per-task opt-out** — disable deduplication for individual tasks with the `deduplication` label.
+- **Startup resilience** — automatic reconnection with exponential backoff if Redis is unavailable at broker startup.
 
 ## License
 

docs/usage.md

@@ -21,6 +21,8 @@ broker = ListQueueBroker("redis://localhost:6379").with_middlewares(
 | `default_deduplication` | `bool` | `True` | Whether deduplication is enabled for all tasks by default. Set `False` to opt-in per task instead of opting out. |
 | `default_ttl` | `int` | `300` | Default lock TTL in seconds. Overridden per task with the `deduplication_ttl` label. |
 | `key_prefix` | `str` | `"taskiq:deduplication"` | Prefix for all Redis lock keys. |
+| `startup_retries` | `int` | `3` | Number of connection attempts during broker startup. |
+| `startup_retry_delay` | `float` | `1.0` | Base delay in seconds between retries (exponential backoff: delay × 2^n). |
 
 ```python
 broker = ListQueueBroker("redis://localhost:6379").with_middlewares(
@@ -29,10 +31,29 @@ broker = ListQueueBroker("redis://localhost:6379").with_middlewares(
         default_deduplication=True,
         default_ttl=60,
         key_prefix="myapp:dedup",
+        startup_retries=5,
+        startup_retry_delay=0.5,
     ),
 )
 ```
 
+## Startup resilience
+
+On startup the middleware verifies the Redis connection with a `PING`. If Redis is
+temporarily unavailable, it retries with exponential backoff.
+After all attempts are exhausted a `ConnectionError` is raised and the broker
+fails to start.
+
+Adjust `startup_retries` and `startup_retry_delay` to suit your deployment:
+
+```python
+RedisDeduplicationMiddleware(
+    redis_url="redis://localhost:6379",
+    startup_retries=5,
+    startup_retry_delay=2.0,
+)
+```
+
 ## How it works
 
 When a task is dispatched, the middleware acquires a Redis lock keyed on the task's

src/taskiq_deduplication/middleware.py

@@ -1,7 +1,8 @@
+import asyncio
 import hashlib
 import json
 import logging
-from typing import Any
+from typing import Any, Awaitable, cast
 
 from redis.asyncio import Redis
 from taskiq import TaskiqMessage, TaskiqResult
@@ -42,15 +43,43 @@ class RedisDeduplicationMiddleware(TaskiqMiddleware):
         default_deduplication: bool = True,
         default_ttl: int = 300,
         key_prefix: str = "taskiq:deduplication",
+        startup_retries: int = 3,
+        startup_retry_delay: float = 1.0,
     ) -> None:
         self.redis_url = redis_url
         self.default_deduplication = default_deduplication
         self.default_ttl = default_ttl
         self.key_prefix = key_prefix
+        self.startup_retries = startup_retries
+        self.startup_retry_delay = startup_retry_delay
         self._redis: Redis | None = None
 
     async def startup(self) -> None:
+        last_error: BaseException | None = None
+        for attempt in range(self.startup_retries):
+            try:
                 self._redis = Redis.from_url(self.redis_url)
+                await cast(Awaitable[bool], self._redis.ping())
+                return
+            except Exception as exc:
+                last_error = exc
+                if attempt < self.startup_retries - 1:
+                    delay = self.startup_retry_delay * (2**attempt)
+                    logger.warning(
+                        "Failed to connect to Redis (attempt %d/%d): %s. "
+                        "Retrying in %.1fs...",
+                        attempt + 1,
+                        self.startup_retries,
+                        exc,
+                        delay,
+                    )
+                    await asyncio.sleep(delay)
+        logger.error(
+            "Failed to connect to Redis after %d attempts.", self.startup_retries
+        )
+        raise ConnectionError(
+            f"Could not connect to Redis after {self.startup_retries} attempts"
+        ) from last_error
 
     async def shutdown(self) -> None:
         if self._redis is not None:

src/taskiq_deduplication/utils.py

@@ -1,12 +1,7 @@
-from collections.abc import Awaitable
-from typing import cast
-
 from redis.asyncio import Redis
+from redis.commands.core import AsyncScript
 
-
-async def check_and_delete(redis: Redis, key: str, owner: str) -> bool:
-    """Delete *key* only if its value equals *owner*. Returns True if deleted."""
-    release_script = """
+RELEASE_LUA_SCRIPT = """
 if redis.call('get', KEYS[1]) == ARGV[1] then
     return redis.call('del', KEYS[1])
 else
@@ -14,5 +9,18 @@ async def check_and_delete(redis: Redis, key: str, owner: str) -> bool:
 end
 """
 
-    released = await cast(Awaitable[int], redis.eval(release_script, 1, key, owner))
+
+async def check_and_delete(redis: Redis, key: str, owner: str) -> bool:
+    """Delete *key* only if its value equals *owner*.
+
+    Args:
+        redis: Async Redis client.
+        key: Lock key to delete.
+        owner: Expected value of the key (task_id).
+
+    Returns:
+        True if the key was deleted, False otherwise.
+    """
+    script: AsyncScript = redis.register_script(RELEASE_LUA_SCRIPT)
+    released: int = await script(keys=[key], args=[owner])
     return bool(released)

tests/test_middleware.py

@@ -332,3 +332,75 @@ class TestLifecycle:
         mw = RedisDeduplicationMiddleware(redis_url="redis://localhost")
         with pytest.raises(RuntimeError, match="startup"):
             await mw.pre_send(make_message())
+
+
+class TestStartupRetry:
+    @pytest.mark.anyio
+    async def test_startup_succeeds_after_retries(self):
+        mw = RedisDeduplicationMiddleware(
+            redis_url="redis://localhost",
+            startup_retries=3,
+            startup_retry_delay=0.01,
+        )
+        with patch("redis.asyncio.Redis.from_url") as mock_from_url:
+            mock_client = AsyncMock()
+            mock_client.ping.side_effect = [
+                ConnectionError("fail"),
+                ConnectionError("fail"),
+                None,
+            ]
+            mock_from_url.return_value = mock_client
+            await mw.startup()
+            assert mw._redis is mock_client
+            assert mock_client.ping.call_count == 3
+
+    @pytest.mark.anyio
+    async def test_startup_raises_after_all_retries_exhausted(self):
+        mw = RedisDeduplicationMiddleware(
+            redis_url="redis://localhost",
+            startup_retries=2,
+            startup_retry_delay=0.01,
+        )
+        with patch("redis.asyncio.Redis.from_url") as mock_from_url:
+            mock_client = AsyncMock()
+            mock_client.ping.side_effect = ConnectionError("refused")
+            mock_from_url.return_value = mock_client
+            with pytest.raises(ConnectionError, match="2 attempts"):
+                await mw.startup()
+            assert mock_client.ping.call_count == 2
+
+    @pytest.mark.anyio
+    async def test_startup_no_retry_on_first_success(self):
+        mw = RedisDeduplicationMiddleware(
+            redis_url="redis://localhost",
+            startup_retries=3,
+            startup_retry_delay=0.01,
+        )
+        with patch("redis.asyncio.Redis.from_url") as mock_from_url:
+            mock_client = AsyncMock()
+            mock_from_url.return_value = mock_client
+            await mw.startup()
+            mock_client.ping.assert_called_once()
+
+    @pytest.mark.anyio
+    async def test_startup_retry_delay_exponential(self):
+        mw = RedisDeduplicationMiddleware(
+            redis_url="redis://localhost",
+            startup_retries=3,
+            startup_retry_delay=0.01,
+        )
+        with (
+            patch("redis.asyncio.Redis.from_url") as mock_from_url,
+            patch("asyncio.sleep", new_callable=AsyncMock) as mock_sleep,
+        ):
+            mock_client = AsyncMock()
+            mock_client.ping.side_effect = [
+                ConnectionError("fail"),
+                ConnectionError("fail"),
+                None,
+            ]
+            mock_from_url.return_value = mock_client
+            await mw.startup()
+            assert mock_sleep.call_count == 2
+            assert mock_sleep.call_args_list[0].args[0] == 0.01
+            assert mock_sleep.call_args_list[1].args[0] == 0.02