How do I debug edge function requests not reaching my origin?

Here’s a practical checklist to debug edge function requests not reaching your origin.

1) Confirm the request actually hits the edge function

Add logging at the very start of the edge handler.

• Log method, URL, headers you care about, and a unique request ID.
• Return a temporary marker response if needed.

Example idea:

• “edge received request”
• request path
• x-request-id

If you don’t see logs, the problem is before your function:

• route not matched
• deployment not active
• function disabled
• auth/WAF blocking
• wrong hostname or path

2) Verify routing and match patterns

Check:

• domain/hostname
• path pattern
• method restrictions
• function association order

Common issue:

• The edge function is attached to /api/*, but the request goes to /api or /v1/api
• A default route or rewrite sends traffic somewhere else
• A different edge rule is taking precedence

3) Check whether the function is short-circuiting

Your edge code may be:

• returning a response directly
• failing before proxying
• rewriting to an invalid origin path
• not forwarding the request body/headers correctly

Look for:

• return new Response(...)
• missing fetch(originUrl, request) or equivalent
• accidental early exit on conditionals

4) Inspect origin forwarding logic

If the edge function proxies to origin, confirm:

• origin URL is correct
• protocol is correct (https vs http)
• hostname resolves
• path is preserved or intentionally rewritten
• query string is preserved
• headers required by origin are forwarded

Watch out for:

• using the wrong header set
• dropping Host
• altering Authorization
• not forwarding cookies if needed
• stripping Content-Type
• body already consumed before forwarding

5) Check for origin-side blocks

The request may arrive but be rejected by origin, so it looks like it never reached it.

Inspect origin logs and status codes:

• 403 from origin/WAF
• 404 from origin routing
• 502/504 from upstream
• TLS/SSL handshake failures

Also verify:

• IP allowlists
• firewall rules
• bot protection
• auth middleware
• rate limits

6) Add end-to-end identifiers

Use a request ID across edge and origin.

• At edge: generate or forward x-request-id
• At origin: log that same ID

This tells you exactly where the request stops.

7) Use curl to isolate layers

Test directly against:

1. the public edge URL
2. the origin URL
3. the edge with special headers

Examples:

• curl -v https://edge.example.com/path
• curl -v https://origin.example.internal/path

Compare:

• status codes
• redirects
• headers
• timing

8) Check response timing and failures

If the edge function times out, origin may never be contacted or the response never returns.

Look for:

• execution timeout
• upstream timeout
• DNS resolution errors
• TLS errors
• connection refused

Log around the fetch call:

• before fetch
• after fetch
• catch block error message

9) Confirm body handling

For POST/PUT/PATCH requests:

• Ensure the body is still readable when proxied
• Some runtimes allow the body to be read only once
• Clone the request if needed

If body handling is wrong, the origin may receive an empty body or the proxy may fail.

10) Review platform-specific edge limitations

Some edge environments limit:

• outbound network access
• certain ports
• request body size
• header size
• supported APIs
• custom TLS behavior

Check platform docs for:

• function runtime constraints
• proxy/fetch support
• origin connection requirements

11) Use temporary debug headers

Add headers from edge to origin:

• x-edge-debug: true
• x-edge-routed-by: my-function
• x-request-id: ...

Then inspect whether origin receives them.

12) If you have CDN/WAF, check their logs too

If your stack is: Client → CDN → Edge Function → Origin

then any of these could block the request:

• CDN cache rule
• WAF rule
• bot mitigation
• function invocation failure
• origin shield / upstream config

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Quick triage flow

1. No edge logs? Route/deployment issue.
2. Edge logs but no origin logs? Proxy/origin connectivity issue.
3. Origin logs but no expected response? Origin app/routing/auth issue.
4. Works with direct origin curl but not through edge? Edge rewrite/headers/body issue.

If you want, I can also give you:

• a platform-specific checklist for Cloudflare / Fastly / AWS CloudFront / Vercel / Netlify
• a sample debug proxy edge function
• help interpreting specific logs or code if you paste them here