Merge remote-tracking branch 'magordon/patch-1' into errors

Author: ggailey777

articles/azure-functions/TOC.yml

@@ -855,6 +855,8 @@
             href: errors-diagnostics/diagnostic-events/azfd0002.md
           - name: AZFD0003
             href: errors-diagnostics/diagnostic-events/azfd0003.md
+          - name: AZFD0004
+            href: errors-diagnostics/diagnostic-events/azfd0004.md
     - name: host.json 2.x reference
       href: functions-host-json.md
     - name: host.json 1.x reference

articles/azure-functions/errors-diagnostics/diagnostic-events/azfd0004.md

@@ -0,0 +1,35 @@
+---
+title: "AZFD0004: Host ID collision"
+titleSuffix: "Azure Functions"
+description: "AZFD0004: Host ID collision"
+author: madelinegordon
+ms.author: magordon
+ms.topic: troubleshooting
+ms.date: 01/19/2023
+---
+
+# AZFD0004: Host ID collision
+
+This event occurs when you have multiple Function Apps sharing a single storage account they're each using the same host ID, which is usually autogenerated.
+
+| | Value |
+|-|-|
+| **Event ID** |AZFD0004|
+| **Category** |[Usage]|
+| **Severity** |Error|
+
+## Event description
+
+A host ID collision can occur when you have more than one function app or slots sharing the same storage account and using the same host ID. For example, if you have multiple apps or slots with names longer than 32 characters and the first 32 characters are shared, both generated host ID values may be the same due to truncation. 
+
+When multiple apps have the same host ID, the resulting collision can result incorrect behaviors. For example, some triggers, like timer and Blob Storage, store tracking info by host ID. This can result in incorrect behavior when the host can't differentiate between apps by host ID. When this collision is detected, an error (hard failure) is logged and the host is shut down.
+
+For more information, see [host ID considerations](../../../storage-considerations.md#host-id-considerations).
+
+## Options for addressing collisions:
+- Connection your function app at a different storage account by changing the [AzureWebJobsStorage](../../../functions-app-settings.md#azurewebjobsstorage) application setting.
+- Rename your function app to something less than 32 characters in length. This changes the host ID generated for the app and removes the collision.
+- Provide explicit host ID values for your function apps or slots so they no longer conflict. For more information, see [host ID considerations](../../../storage-considerations.md#host-id-considerations).
+
+## When to suppress the event
+This event should not be suppressed.