tls: first record does not look like a TLS handshake will retry.

[agardnerIT]

Similar to #310 I've cloned the repo and build the server:

git clone https://github.com/open-telemetry/opamp-go
cd opamp-go
make build-example-server
cd internal/examples/server/bin
./server

Then I run my collector in a new terminal:

./otelcol-contrib --config=config.yaml

and see:

./otelcol-contrib --config=collector-config.yaml
2025-03-29T14:44:18.393+1000    info    service@v0.121.0/service.go:193 Setting up own telemetry...
2025-03-29T14:44:18.394+1000    info    service@v0.121.0/service.go:258 Starting otelcol-contrib...     {"Version": "0.121.0", "NumCPU": 8}
2025-03-29T14:44:18.394+1000    info    extensions/extensions.go:40     Starting extensions...
2025-03-29T14:44:18.394+1000    info    extensions/extensions.go:44     Extension is starting...        {"otelcol.component.id": "opamp", "otelcol.component.kind": "Extension"}
2025-03-29T14:44:18.422+1000    info    extensions/extensions.go:61     Extension started.      {"otelcol.component.id": "opamp", "otelcol.component.kind": "Extension"}
2025-03-29T14:44:18.422+1000    error   opampextension@v0.121.0/opamp_agent.go:138      Failed to connect to the OpAMP server   {"otelcol.component.id": "opamp", "otelcol.component.kind": "Extension", "error": "tls: first record does not look like a TLS handshake"}
github.com/open-telemetry/opentelemetry-collector-contrib/extension/opampextension.(*opampAgent).Start.func3
        github.com/open-telemetry/opentelemetry-collector-contrib/extension/opampextension@v0.121.0/opamp_agent.go:138
github.com/open-telemetry/opamp-go/client.(*wsClient).tryConnectOnce
        github.com/open-telemetry/opamp-go@v0.19.0/client/wsclient.go:239
github.com/open-telemetry/opamp-go/client.(*wsClient).ensureConnected
        github.com/open-telemetry/opamp-go@v0.19.0/client/wsclient.go:282
github.com/open-telemetry/opamp-go/client.(*wsClient).runOneCycle
        github.com/open-telemetry/opamp-go@v0.19.0/client/wsclient.go:326
github.com/open-telemetry/opamp-go/client.(*wsClient).runUntilStopped
        github.com/open-telemetry/opamp-go@v0.19.0/client/wsclient.go:412
github.com/open-telemetry/opamp-go/client/internal.(*ClientCommon).StartConnectAndRun.func1
        github.com/open-telemetry/opamp-go@v0.19.0/client/internal/clientcommon.go:208

Where my collector config is (extract):

extensions:
  opamp:
    server:
      ws:
        endpoint: "wss://127.0.0.1:4320/v1/opamp"
        # Disable verification to test locally.
        # Don't do this in production.
        tls:
          insecure_skip_verify: true
service:
  extensions: [opamp]  # Enable the OpAMP extension
  pipelines:
    logs:
    ....

Running all of this locally. I also notice I can't get to the browser UI.

[johannaojeling]

@agardnerIT I can reproduce the error on the opamp-go server when following your steps. It results in the server UI being inaccessible and the below log output:

$ cd opamp-go
$ make build-example-server
$ cd internal/examples/server/bin
$ ./server
2025/04/21 10:41:36.698382 [MAIN] OpAMP Server starting...
2025/04/21 10:41:36.698841 [OPAMP] Could not load TLS config, working without TLS: open ../../certs/certs/ca.cert.pem: no such file or directory
2025/04/21 10:41:36.699214 [MAIN] OpAMP Server running...

The reason is because the ../../certs/certs/ca.cert.pem path should be relative to the directory internal/examples/server and not internal/examples/server/bin.

Try this instead and your server problems should go away:

$ cd opamp-go
$ make build-example-server
$ cd internal/examples/server
$ ./bin/server
2025/04/21 10:43:27.674677 [MAIN] OpAMP Server starting...
2025/04/21 10:43:27.675714 [MAIN] OpAMP Server running...

When running the OTel Collector Contrib v0.121.0 (as your collector logs indicate) with the OpAMP extension like in your config file, I can see the collector successfully listed in the Agents list in the server UI.

[tpaschalis]

cc @agardnerIT does the above solve your problem, can this issue be closed?