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eschabell merged 2 commits into from
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docs: administration: configuring-fluent-bit: document http_server.http1_max_header_size #2817

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22 changes: 20 additions & 2 deletions administration/configuring-fluent-bit/yaml/pipeline-section.md
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Expand Up @@ -169,6 +169,7 @@ plugin-specific behavior.
| `http_server.http2` | Enable HTTP/2 support for the input listener. | `true` |
| `http_server.buffer_max_size` | Set the maximum size of the HTTP request buffer. | `4M` |
| `http_server.buffer_chunk_size` | Set the allocation chunk size used for the HTTP request buffer. | `512K` |
| `http_server.http1_max_header_size` | Set the maximum size of an HTTP/1 request line and headers, including the line-ending characters. Uses binary units: `K`, `KB`, and `KiB` all mean 1,024 bytes, and `M`/`G` scale the same way. `0` selects the default. The `http_server.buffer_max_size` limit still applies. Supported in v5.2 or later. See [HTTP/1 request header limits](#http1-request-header-limits). | `32KiB` |
| `http_server.max_connections` | Set the maximum number of concurrent active HTTP connections. `0` means unlimited. | `0` |
| `http_server.workers` | Set the number of HTTP listener worker threads. | `1` |
| `http_server.ingress_queue_event_limit` | Set the maximum number of deferred ingress queue entries. This setting applies only when `http_server.workers` is greater than `1`. | `8192` |
Expand All @@ -179,9 +180,26 @@ When `http_server.workers` is `1`, Fluent Bit does not use the deferred
ingress queue, so the two `http_server.ingress_queue_*` settings have no
effect.

For backward compatibility, some plugins also accept the legacy aliases `http2`, `buffer_max_size`, `buffer_chunk_size`, `max_connections`, and `workers`.
For backward compatibility, some plugins also accept the legacy aliases `http2`, `buffer_max_size`, `buffer_chunk_size`, `max_connections`, and `workers`. The other `http_server.*` keys, such as `http_server.http1_max_header_size`, have no alias and must use the full name.

These plugins also pause and resume the shared listener in response to [backpressure](../../backpressure.md#pause-behavior-for-http-based-inputs). While an input is paused, Fluent Bit accepts and immediately closes incoming connections instead of buffering the requests, so clients must retry.
All inputs that use the shared listener also pause and resume it in response to [backpressure](../../backpressure.md#pause-behavior-for-http-based-inputs). While an input is paused, Fluent Bit accepts and immediately closes incoming connections instead of buffering the requests, so clients must retry.

#### HTTP/1 request header limits
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Fluent Bit reads the request line and headers of each HTTP/1 request before it processes the request. The `http_server.http1_max_header_size` limit counts the request line, the headers, and the blank line that ends them. Fluent Bit closes the connection without a response when:

- The request line and headers reach `http_server.http1_max_header_size` without the blank line that ends them. This limit is new in v5.2.
- The request method is longer than 11 bytes.
- The request target contains a carriage return or line feed.
- The protocol version doesn't start with `HTTP/1.`.

If the request reaches `http_server.buffer_max_size` first, Fluent Bit responds with `413 Request Entity Too Large` and closes the connection. Setting `http_server.http1_max_header_size` higher than `http_server.buffer_max_size` has no effect beyond the buffer limit.

Earlier versions don't enforce a separate header size limit; only `http_server.buffer_max_size`, `4M` by default, bounds the request line and headers. In v5.2 or later, requests whose headers reach the `32KiB` default, for example because of large cookies or tokens, are dropped without a response or a log message. If your clients send large headers, raise `http_server.http1_max_header_size` before you upgrade.

These checks apply to HTTP/1 requests, including HTTP/1.1 requests that ask to upgrade to HTTP/2. Connections that start directly with the HTTP/2 connection preface aren't affected.

Fluent Bit fails to start if `http_server.http1_max_header_size` isn't a number, is negative, or has a suffix other than `K`, `KB`, `KiB`, `M`, `MB`, `MiB`, `G`, `GB`, or `GiB`, and logs `[http_server] invalid http_server.http1_max_header_size`. The suffixes aren't case-sensitive and must follow the number without a space. Fractional values are truncated to whole bytes, and values that truncate to `0` select the default.

### Incoming `OAuth 2.0` `JWT` validation settings

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