APIM Error: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host

Question

We are getting the following error, Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host
Our Backend is hosted on AKS and is behind nginx. When we try to process a file which takes more than 5 minutes it throws out this error, we checked on nginx level and always got response. But when went through APIM it errors out and gives below error message.

We have increased the timeouts as well, also find the policy xml below.
<policies>

<inbound>

<base/>

</inbound>

<backend>

<retry condition="@(context.Response.StatusCode == 0 || context.Response.StatusCode >= 500)" count="10" interval="10" max-interval="100" delta="10" first-fast-retry="false">

<forward-request timeout="1200" buffer-response="false" buffer-request-body="true"/>

</retry>

</backend>

<outbound>

<base/>

</outbound>

<on-error>

<base/>

</on-error>

</policies>

Answer 1

Hi @Mishra, Nitin Greetings! Welcome to Microsoft Q&A forum. Thank you for posting this question here.

This is a limitation in Azure infrastructure. Even though, you set timeout="1200" in the forward-request policy, Values greater than 240 seconds may not be honored, because the underlying network infrastructure can drop idle connections after this time. Please refer the documentation on forward-request policy where the below limitation is mentioned.

You can make the backend service end point processing the file asynchronous and return a 202 response and implement some sort of polling mechanism on the backend service to get the status by hitting the end point in periodic intervals. Here is a typical flow to implement this

Please also refer to this comment on the GitHub where a similar issue was discussed.

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