How to avoid delay while swapping slots of a Function app or restarting it.

Question

Hi,

I'm testing slot swapping of a function app that runs an API application.

However, I found response time severely delayed (average:180ms, while swapping or restarting; 7300ms)

I set WEBSITE_WARMUP_PATH, and WEBSITE_SWAP_WARMUP_PING_PATH, but it did not help.

How can I mitigate the delay?

Answer 1

We understand you are trying to cut down on the response time of your app after swapping slots.

This can be achieved one of two ways. You have already tried one of the ways but please read the important note below to ensure you had it configured correctly. If you did have it configured correctly, please see the second option.

• WEBSITE_SWAP_WARMUP_PING_PATH: The path to ping over HTTP to warm up your site. You can specify a custom path that begins with a slash as the value. The default value is /. It is important that the request hits a http page that can generate a 200 response. Note that redirects or authentication pages will likely break this. You may need to place a generic page outside of any authentication pages and then direct the ping to this URL.
• WEBSITE_SWAP_WARMUP_PING_STATUSES: Valid HTTP response codes for the warm-up operation. You can add this app setting with a comma-separated list of HTTP codes. If the returned status code isn't in the list, the warmup and swap operations are stopped. By default, all response codes are valid.

Please let us know the outcome of the above suggestions. We look forward to your reply.