When working with Azure Logic Apps/ Function Apps/ App Service, you might encounter the following error:
“The environment block used to start a process cannot be longer than 65535 bytes. Your environment block is 85754 bytes long. Remove some environment variables and try again.”
This happens because **Azure app settings** are stored as **environment variables**, and Windows enforces a strict 65,535-byte limit on the total size of these variables. If the combined size exceeds this limit, the process fails to start.
Why Does This Happen?
In Azure Logic Apps, this issue typically arises due to:
- Too many app settings defined in the configuration.
- Very large values stored in app settings.
- App settings with Azure Key Vault references, where the **size of the actual secret value** also contributes to the total environment block size.
- Dependencies (e.g., SDKs, connectors) adding long **environment variables** automatically.
Even though Key Vault references are intended to keep secrets secure, the **retrieved secret value** is still counted towards the **app setting size**, potentially leading to this issue.
How to Fix It
1. Identify Large App Settings
To check the total size of app settings in Azure:
- Go to the Azure Portal.
- Navigate to your Logic App → Configuration.
- Review the app settings listed under the Application settings tab.
If you are using Key Vault references, be aware that the actual **size of the secret value** is included in the environment block.
2. Remove or Reduce Unnecessary App Settings
- Delete unused app settings that are no longer required.
- Shorten long values, especially for connection strings, JSON configurations, or large text-based settings.
- Avoid storing large secrets in Key Vault if they are referenced in app settings, as their size still counts towards the limit.
3. Store Large Data in External Services
- Use Azure Key Vault with direct API calls instead of app setting references. This prevents secrets from being loaded as environment variables.
- Use Azure App Configuration for managing configurations separately from app settings.
- Store large JSON configurations or data-heavy settings in Azure Blob Storage or Cosmos DB.
4. Restart the Logic App
After making changes, restart your Logic App for the new settings to take effect.
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