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Async Requests Not Completing

TL;DR

  1. Check that AsyncModeEnabled=true and the request sends the S7PAsyncMode header.
  2. Verify the user profile has async configuration with a valid blob container and Service Bus topic.
  3. If blobs exist but are empty, the critical cause is OutputStream not being cleared — see below.

How async mode works

Client sends request with S7PAsyncMode header
    │
    ▼
Proxy processes normally → if processing exceeds AsyncTriggerTimeout:
    │
    ▼
Proxy returns 202 immediately
    │ (blob URI + SB topic in response body)
    ▼
AsyncWorker writes response → Blob Storage
    │
    ▼
Status update written → Service Bus topic

Step 1 — Verify async is enabled

All three must be true for async to activate:

Condition Setting Env Var
System switch on AsyncModeEnabled=true AsyncModeEnabled
Request header present Header name = AsyncClientRequestHeader (default S7PAsyncMode) set on request
User profile has async config Profile field async-config contains blob container + SB topic —

Step 2 — Check the trigger timeout

AsyncTriggerTimeout (default 10 s) is the time a request must be in flight before async kicks in. If the backend responds in under 10 s, the request is returned synchronously — this is normal.

To force a request to go async sooner, reduce AsyncTriggerTimeout:

Setting Env Var App Config key
Trigger timeout (ms) AsyncTriggerTimeout=<ms> Warm:Async:TriggerTimeout

Step 3 — Check blob storage configuration

AsyncBlobStorageConfig is a composite string:

AsyncBlobStorageConfig=uri=https://mystorageaccount.blob.core.windows.net,mi=true

For managed identity (mi=true), the proxy identity needs Storage Blob Data Contributor on the storage account.

az role assignment create \
  --assignee <principal-id> \
  --role "Storage Blob Data Contributor" \
  --scope "/subscriptions/<sub>/resourceGroups/<rg>/providers/Microsoft.Storage/storageAccounts/<account>"

Step 4 — Check Service Bus configuration

AsyncSBConfig is a composite string:

AsyncSBConfig=cs=<connection-string>,ns=<namespace>,q=requeststatus,mi=true

For managed identity, the proxy identity needs Azure Service Bus Data Sender on the namespace or topic.

Symptom: blobs exist but are empty

Warning

Critical bug (fixed Feb 2026): After the proxy sends the 202 response and closes the client connection, OutputStream must be explicitly set to null. If it is not, GetOrCreateDataStreamAsync() returns the already-closed client stream instead of opening a blob stream, and the backend response is written to nothing.

If you are running a custom build or patched version, verify AsyncWorker.cs contains:

_requestData.Context.Response.Close();
_requestData.OutputStream = null;  // ← CRITICAL — must follow Close()

This line must appear after Response.Close(). Without it, the blob will be created but will remain empty.

Symptom: 202 never arrives — request returns synchronously

  • AsyncTriggerTimeout may be larger than the backend response time. The backend responded before async was triggered.
  • Verify the client is sending the S7PAsyncMode header.

Symptom: 202 arrives but blob URI is never populated

  • Check Service Bus connectivity — the status message (with the blob URI) may not be reaching the client.
  • Check blob container name in the user profile async-config field.
  • Check AsyncBlobWorkerCount — if set to 0 or the workers are all busy, blobs queue up.

Symptom: async request times out with no blob

AsyncTimeout (default 30 min) is the maximum async request lifetime. After this, the request is abandoned. If the backend takes longer than 30 min, increase AsyncTimeout.

Setting Env Var App Config key
Max async lifetime (ms) AsyncTimeout=<ms> Warm:Async:Timeout
Async request TTL after upgrade AsyncTTLSecs=<s> Warm:Async:TTLSecs

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