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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchRetry-After: 0 is valid: it tells a client there is no server-requested delay before a follow-up request. It does not mean the client must retry immediately, keep retrying, or ignore its own safety limits. If your loop is hammering an endpoint, add bounded retries and backoff independently of the header.
What does Retry-After: 0 mean?
RFC 9110 allows Retry-After to contain either an HTTP date or a non-negative integer number of seconds. The integer form uses decimal digits, so 0 is valid and represents zero seconds of requested waiting. The standard describes the field this way: “Servers send the "Retry-After" header field to indicate how long the user agent ought to wait before making a follow-up request.” RFC 9110, §10.2.3.
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The standard specifically discusses the header with 503 Service Unavailable responses, where it indicates the expected period of unavailability, and with 3xx redirections, where it gives a minimum wait before the redirected request. These descriptions explain the server’s delay signal; they do not define a complete retry algorithm for every client.
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Not necessarily. If a client uses the header as its only pacing rule, a zero value can lead it to send the next request immediately. That is a consequence of the client’s implementation, not a requirement that RFC 9110 places on clients. The header supplies a delay value; your application still needs to decide whether the failure is retryable, whether repeating the operation is safe, and how many attempts are allowed.
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Do not assume all HTTP libraries handle zero the same way. Check the documentation or source for the exact library and version you use before relying on its behavior.
Why is my retry loop making requests continuously?
A loop can lose its brakes when it treats every failure as transient and lets Retry-After: 0 set the entire delay. Each failed request then leads to another with no pause, and the cycle can continue indefinitely if there is no attempt limit or deadline. Rapid retries can add load to a service that is already struggling.
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Retry only failures you have classified as transient, and only when the operation can safely be repeated. Google Cloud’s guidance advises checking idempotency and warns against automatically retrying non-idempotent operations. If repetition could create duplicate side effects, use an appropriate idempotency or deduplication mechanism before retrying. Google Cloud Monitoring retry guidance and Google Cloud Storage retry strategy.
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How do I add backoff when the server says zero?
Use the server-provided delay as one input to your policy, not as permission to bypass local safeguards. For an eligible transient failure, a robust client can apply truncated exponential backoff with jitter, while enforcing both a maximum attempt count and an overall deadline. These are implementation recommendations; RFC 9110 defines the header’s meaning but does not prescribe this full client policy.
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- Check retry safety. Retry only if the failure is plausibly transient and repeating the operation is safe, or your application has a suitable idempotency or deduplication mechanism.
- Set hard bounds. Choose a maximum number of attempts and a total elapsed-time deadline. Stop when either limit is reached, regardless of the header value.
- Calculate a local backoff. Increase the delay between attempts exponentially, cap it at a maximum, and add jitter so clients do not all retry together. A zero server delay must not erase this local pacing if your policy is intended to slow retries.
- Respect the header deliberately. Parse either the HTTP-date form or the integer-seconds form. Decide explicitly how the server’s requested delay interacts with local limits and your backoff; the RFC does not specify one universal combination rule.
- Stop when the operation is no longer worth retrying. On reaching the attempt cap or deadline, return or surface the failure instead of starting another request.
Google Cloud Monitoring recommends truncated exponential backoff and limits based on retry count or elapsed time. Google Cloud IAM illustrates delays of 1, 2, and 4 seconds plus a random fraction, with a cap and an overall deadline; those numbers are an example in its guidance, not required constants for every client. Its documentation puts it plainly: “To avoid triggering this issue, we strongly recommend that you use truncated exponential backoff with introduced jitter, which is a standard error-handling strategy for network applications.” Google Cloud Monitoring and Google Cloud IAM.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What if the header is malformed?
RFC 9110 defines an HTTP date and decimal delay-seconds as the valid forms. It does not establish a universal client fallback for malformed values. Treat fallback behavior as a deliberate defensive choice in your implementation: for example, reject the value or fall back to your bounded local policy, while preserving the attempt and deadline limits.
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What should I verify in my implementation?
- The retry condition is limited to transient failures rather than every error response.
- The operation is safe to repeat, or duplicate effects are prevented.
- A zero delay cannot bypass your chosen local pacing policy.
- Attempts and total elapsed time are both bounded.
- Backoff is capped, and jitter is used where synchronized retries are a concern.
- Behavior for HTTP-date, integer-seconds, and malformed header values is intentional and tested for your specific client library and version.
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