Request Retry Logic: Mermaid Flowchart Diagram

About Source

Request retry logic is a client-side resilience pattern that automatically re-attempts failed requests using a backoff strategy, improving success rates for transient failures without overwhelming an already-struggling upstream service.

What the diagram shows

This flowchart models the complete retry decision tree:

1. Send request: the client sends the initial request to the upstream service. 2. Evaluate response: a successful response (2xx) exits the loop immediately. 3. Classify error: not all failures are retriable. 4xx client errors (e.g., 400 Bad Request, 401 Unauthorized, 404 Not Found) indicate the request itself is malformed — retrying it won't help. 429 Too Many Requests and 5xx server errors are candidates for retry. 4. Check retry budget: the client tracks the attempt count against a configured maximum (e.g., 3 attempts). Exhausted retries surface the error to the caller. 5. Compute backoff: the wait time between retries follows exponential backoff — base * 2^attempt — with added jitter to prevent thundering herd when many clients retry simultaneously. 6. Wait and retry: after the backoff period, the request is re-attempted.

Why this matters

Without retry logic, transient network blips or brief service restarts cause user-visible errors that could be silently recovered. Without a backoff strategy, naive retries can amplify load on a struggling service — the opposite of what you want. Exponential backoff with jitter is the industry-standard approach, recommended by AWS, Google, and Netflix in their resilience guidelines.

Retries should always pair with a Circuit Breaker Pattern — once a service is known to be down, the circuit opens and retries are skipped entirely. For webhook-specific retry strategies, see Webhook Retry Strategy. The Rate Limiting Architecture explains the 429 responses that trigger retries on the server side.

Frequently asked questions

Request retry logic is a client-side resilience pattern that automatically re-attempts failed HTTP requests using a backoff strategy. It improves success rates for transient failures — network blips, brief service restarts, or temporary overloads — without requiring manual intervention or surfacing spurious errors to the user.

After a failed request, the client first classifies the error: 4xx client errors (400, 401, 404) are not retriable because retrying won't fix a malformed request. 5xx server errors and 429 responses are candidates for retry. If the attempt count is below the configured maximum, the client waits for an exponential backoff period — base delay multiplied by 2 to the power of the attempt number — plus a random jitter value, then re-sends the request.

Always use backoff with jitter for any retry logic in production. Backoff prevents a struggling service from being immediately hammered with retries. Jitter — random variation in the wait time — prevents the thundering herd effect, where many clients all backed off for the same duration and simultaneously retry at the same moment, creating a traffic spike at a predictable interval.

A common mistake is retrying 4xx responses — a 400 Bad Request will never succeed no matter how many times it is retried. Another frequent error is not setting a maximum retry count, creating an infinite retry loop. Teams also forget to make the operation being retried idempotent — if a charge request is retried after the first attempt succeeded but the response was lost, the customer may be double-charged.

mermaid

flowchart TD
    A([Send request]) --> B{Response received?}
    B -- No response / timeout --> C[Classify as retriable error]
    B -- Response received --> D{HTTP status code}

    D -- 2xx Success --> E([Return success to caller])
    D -- 4xx Client Error --> F([Return error - do not retry])
    D -- 429 Too Many Requests --> C
    D -- 5xx Server Error --> C

    C --> G{Retry budget remaining?}
    G -- No retries left --> H([Return final error to caller])
    G -- Retries available --> I[Increment attempt counter]
    I --> J[Compute exponential backoff with jitter]
    J --> K[Wait backoff duration]
    K --> L[Re-send request]
    L --> B