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[APM] Add known issue for HTTP/2 strict client framing failures #4979

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carsonip merged 6 commits into from
Apr 21, 2026
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[APM] Add known issue for HTTP/2 strict client framing failures #4979

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31fb194
docs: add APM HTTP/2 strict client known issue for 8.x
carsonip Apr 17, 2026
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docs: align HTTP/2 known-issue wording with apm-server
carsonip Apr 17, 2026
e13e68d
docs: use source wording for HTTP/2 workaround
carsonip Apr 17, 2026
4d28043
docs: explicitly label HTTP/2 guidance as workaround
carsonip Apr 17, 2026
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docs: align workaround section with known-issues prose style
carsonip Apr 17, 2026
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carsonip Apr 21, 2026
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22 changes: 22 additions & 0 deletions docs/en/observability/apm/known-issues.asciidoc
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Expand Up @@ -21,6 +21,28 @@ _Versions: XX.XX.XX, YY.YY.YY, ZZ.ZZ.ZZ_
// If applicable, link to fix
////

[discrete]
== HTTP/2 connections can fail with strict clients due to framing errors

_Elastic Stack versions: >=8.19.12 and <8.19.15_

APM Server can fail HTTP/2 requests from strict clients (for example, curl/nghttp2) after ALPN negotiates `h2`.

In affected versions, APM Server can send inconsistent SETTINGS values at connection start (an initial empty/default SETTINGS frame followed by a different SETTINGS set), and strict clients treat that sequence as an HTTP/2 protocol error and close the connection.

When this occurs, clients can report framing/connection errors such as `Error in the HTTP2 framing layer` or `Failure when receiving data from the peer`. Browser-based HTTP requests from the RUM agent can also fail with `net::ERR_HTTP2_PROTOCOL_ERROR`.

When clients close the HTTP/2 connection due to this issue, APM Server logs an error: `http2: received GOAWAY [FrameHeader GOAWAY len=66], starting graceful shutdown`.
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For more information, check https://github.com/elastic/apm-server/issues/20887[issue #20887].

There are two workarounds:

* Use HTTP/1.1 to communicate with APM Server on affected versions.
* If clients require HTTP/2, place a non-strict load balancer in front of APM Server and terminate HTTP/2 at the load balancer (for example, on some load balancers this can be done by switching from TCP mode to HTTP mode).

This bug will be fixed in 8.19.15.

[discrete]
== Tail Sampling may not compact / expired TTLs as quickly as desired, causing increased storage usage.

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