This article will discuss how to set a larger allowed Max Header Size than the default 8 KB. In most cases, 8 KB is more then plenty, but in some circumstances it may be required to increase this limit.
In some cases, you may receive an error such as the following in the SSG logs when the response header size is larger than 8 KB:
com.l7tech.server.message: Message was not processed: Undefined (-1)" along with a java.lang.ArrayIndexOutOfBoundsException exception.
Or you may receive the following response to requests that have a header size larger than 8 KB, which would be a client-seen response and not logged in the SSG logs:
HTTP Error 400 Bad Request
This article applies to all supported API Gateway versions.
The underling HTTP engine used by the Gateway has a default header size of 8K, anything over this size will cause these errors for both incoming and outgoing.
This value can be increased for a particular listen port by setting an advanced property 'maxHttpHeaderSize' on the listen port. To do this, follow the instructions below:
In the Listen Port Properties window, select the Advanced tab, then the Add button to add an advanced property to the port.
After the steps above are completed, the Listen Port Properties (Advanced tab) should look similar to the image below:
Please note that our testing in Broadcom does not go to large header sizes, so if you are setting it a lot higher you will need to be careful to run your own load testing to see if there is any negative impact to your environment. If the traffic using header sizes above 8 KB is infrequent then this will likely not be a problem, but we would strongly recommend load testing properly before moving that change to a production environment.
Product documentation on the Listen Port Advanced Properties can be found here: https://techdocs.broadcom.com/us/en/ca-enterprise-software/layer7-api-management/api-gateway/10-0/security-configuration-in-policy-manager/tasks-menu-security-options/manage-listen-ports/listen-port-properties.html#concept.dita_b2bd9924f304a78cae8f4dee3631ccb27b5d47cb_ConfiguringtheAdvancedTab