400 HTTP message contains more than the configured limit of 64 headers

During Friday 8/12 CET we occasionally got 400 response “HTTP message contains more than the configured limit of 64 headers” when making GET requests. Content-Type header was “text/plain” we expected “application/json”.

What is the cause of that?

The same requests have suceeded before and are successful now, but we’d like to know what caused this?

Hi @Sandraa, sorry for any inconvenience this caused or time spent investigating. This was due to new infrastructure we are testing to improve latency, among other benefits.

We’ve always had the 64 header limit, however, the new system adds some headers which pushed some existing requests over the limit. We have increased our limits to prevent this from a happening in the future.

As we get closer to rolling it out, we will share more details about the new infrastructure soon in the Changelog category of the forum.


Okay thanks, unfortunetaly it caused us some issues which we’d like to avoid in the future. Will the new infrastructure affect format or simliar of api requests and responses?

@Sandraa I’m sorry it caused issues. Could you direct message me to share more about the issues it caused and any business impact? We take breaking apps like this seriously – learning more will help us prevent it from happening in the future.

In terms of future impact when we roll this out, it should not affect requests with lots of headers that are currently succeeding. We have increased the CDN header limits and removed some of the default headers it adds that we don’t need.

One potentially breaking change will be GET requests that have bodies. Historically, our API has been lenient in accepting GET requests with a body, simply discarding the body content. This will no longer be the case. Once we migrate to the CDN, to conform more closely to HTTP specifications, any GET requests that include a body will be rejected with an HTTP 403 error response.

We added logging to see which apps are currently doing this. We will email app owners prior to the change to let them know they need to make this fix.

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