Redis is unavailable during peak traffic. How should the API behave?

Handle Redis outage with fallback and degraded mode

Explains how an API behaves when Redis is unavailable and which cache usages can safely fall back.

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TL;DR

If Redis is only used as a read-through cache, the API can often treat failures as cache misses and read from the database. But it must protect the database because a Redis outage can suddenly send much more traffic to the source. If Redis holds session state, rate-limit counters, locks, or workflow state, the fallback behavior needs a more explicit design.

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Dependency failure, fallback reads, degraded behavior, source protection, circuit breakers, and user-facing impact.

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Why this question matters
A Redis outage reveals whether each usage is optional acceleration, security control, coordination, or undeclared state. Fallback and fail-closed decisions must be defined per usage before peak traffic reaches the source system.
If Redis is only used as a read-through cache, the API can often treat failures as cache misses and read from the database. But it must protect the database because a Redis outage can suddenly send much more traffic to the source. If Redis holds session state, rate-limit counters, locks, or workflow state, the fallback behavior needs a more explicit design.
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I would classify each Redis usage. For product data cache, fallback to source with rate limits or degraded pages may be acceptable. For sessions, users may need to reauthenticate or the app may need a durable session store. For rate limiting, the safe fallback might be fail-closed for risky endpoints or a local temporary limiter for low-risk traffic. For locks and coordination, continuing blindly can create duplicate work.

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Details

Assuming Redis can fail without any user impact.
Falling back to the database with no source protection.
Treating sessions, locks, counters, and read cache the same way.
Retrying Redis aggressively during an outage.

Redis is unavailable during peak traffic. How should the API behave?

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Redis is unavailable during peak traffic. How should the API behave?

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