add libotel for tests

[remicollet]

When otel support is enable, libnxt.a needs libotel.a

Without this patch, when building tests

 LD     build/unit_websocket_chat
/usr/bin/ld: build/lib/libnxt.a(nxt_router.o): in function `nxt_router_conf_create':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_router.c:2217:(.text+0x73c8): undefined reference to `nxt_otel_rs_init'
/usr/bin/ld: /builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_router.c:2221:(.text+0x755f): undefined reference to `nxt_otel_rs_uninit'
/usr/bin/ld: build/lib/libnxt.a(nxt_http_request.o): in function `nxt_http_request_create':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_http_request.c:289:(.text+0x9dc): undefined reference to `nxt_otel_rs_is_init'
/usr/bin/ld: build/lib/libnxt.a(nxt_otel.o): in function `nxt_otel_propagate_header':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:72:(.text+0xe8): undefined reference to `nxt_otel_rs_copy_traceparent'
/usr/bin/ld: /builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:93:(.text+0x14d): undefined reference to `nxt_otel_rs_add_event_to_trace'
/usr/bin/ld: build/lib/libnxt.a(nxt_otel.o): in function `nxt_otel_trace_and_span_init':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:270:(.text+0x280): undefined reference to `nxt_otel_rs_get_or_create_trace'
/usr/bin/ld: build/lib/libnxt.a(nxt_otel.o): in function `nxt_otel_span_add_headers':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:146:(.text+0x340): undefined reference to `nxt_otel_rs_add_event_to_trace'
/usr/bin/ld: /builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:150:(.text+0x382): undefined reference to `nxt_otel_rs_add_event_to_trace'
/usr/bin/ld: /builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:152:(.text+0x3af): undefined reference to `nxt_otel_rs_add_event_to_trace'
/usr/bin/ld: build/lib/libnxt.a(nxt_otel.o): in function `nxt_otel_span_add_body':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:204:(.text+0x48f): undefined reference to `nxt_otel_rs_add_event_to_trace'
/usr/bin/ld: build/lib/libnxt.a(nxt_otel.o): in function `nxt_otel_span_collect':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:245:(.text+0x4dc): undefined reference to `nxt_otel_rs_send_trace'
/usr/bin/ld: build/lib/libnxt.a(nxt_otel.o): in function `nxt_otel_span_add_status':
/builddir/build/BUILD/unit-1.34.0-build/unit-27bde184dedcbf687db2f314c60c037623318a8d/src/nxt_otel.c:230:(.text+0x553): undefined reference to `nxt_otel_rs_add_event_to_trace'

[remicollet]

Notice: this is related to RPM build where -Wl,-z,now is used, so requiring all symbols to be resolved at link time

[ac000]

Yeah, we noticed this...

There are a number of issues with --otel

[remicollet]

There are a number of issues with --otel

Do you count as issue

• size of sources x 33 (with vendored rust libraries to allow offline build)
• size of binary x 8 (1.3M to 11 M for unitd)
• time of build x 7 (without download)

;)

[ac000]

It is certainly less than ideal.

Unfortunately there is no C API for OTEL, there is a C++ API, but that is supposedly horrendous...

In my mind, it would have been possible to create a thin C wrapper (exposing just the bits we need) around the C++ API...

[thresheek]

And for C++ libraries, it's also less than ideal due to the amount of dependencies they have. It's at least:

• abseil-cpp
• protobuf
• grpc

It's not that different size-wise in a resulting binary from the Rust version, and build times are even worse. We have the exact same problem in NGINX otel implementation.

[ac000]

But at least there are distro packages for those things already so no need to build any of that, it would just be building the C wrapper...

[thresheek]

It really, really depends on a distro and its version. It's going to get better though, that's for sure.

[thresheek]

I think this patch is good on it's own, although I'd move $(NXT_OTEL_LIB_LOC) to the position right after $NXT_BUILD_DIR/lib/$NXT_LIB_STATIC (probably next line), since it's out responsibility to provide proper dependency resolution order here.

[ac000]

Commit subject and message would also need tweaking to better describe the actual issue...

Actually this should probably be combined with thresheek@18381b1