Nested labels are indexed as `[object Object]`

[afharo]

Describe the bug

When the agent is set up with nested global labels:

• ELASTIC_APM_GLOBAL_LABELS=myObject.myKeyA=A,myObject.myKeyB.mySubKeyB=B
• The same applies if using globalLabels in the init config.

The resulting indexed transaction looks like labels.myObject: [object Object].

In comparison, the Go agent indexes the transaction with labels.myObject_myKeyA: A and labels.myObject_myKeyB_mySubKeyB: B.

To Reproduce

Steps to reproduce the behavior:

1. Use this config ELASTIC_APM_GLOBAL_LABELS=myObject.myKeyA=A,myObject.myKeyB.mySubKeyB=B (or via globalLabels in the init config.
2. Report a few transactions
3. Take a look at the transaction metadata
4. See labels.myObject: [object Object]

Expected behavior

I'd expect parity with what other agents do. The Go client replaces the dots with underscores to flatten the labels.

Also, the apm.setLabel and apm.addLabel APIs suggest that the dots are replaced with underscores (docs).

Environment (please complete the following information)

Not relevant

How are you starting the agent? (please tick one of the boxes)

• Calling agent.start() directly (e.g. require('elastic-apm-node').start(...))
• Requiring elastic-apm-node/start from within the source code
• Starting node with -r elastic-apm-node/start

Additional context

Agent config options:

Click to expand

As logged by the agent:

{"log.level":"info","@timestamp":"2024-06-20T16:37:50.649Z","log.logger":"elastic-apm-node","ecs.version":"8.10.0","agentVersion":"4.7.0","env":{"pid":37023,"proctitle":"/Users/afharo/.nvm/versions/node/v20.13.1/bin/node","os":"darwin 23.5.0","arch":"arm64","host":"ip-192-168-86-178.eu-central-1.compute.internal","timezone":"UTC+0200","runtime":"Node.js v20.13.1"},"config":{"active":{"source":"start","value":true},"breakdownMetrics":{"source":"start","value":true},"centralConfig":{"source":"start","value":false},"contextPropagationOnly":{"source":"start","value":true},"environment":{"source":"start","value":"development"},"globalLabels":{"source":"start","value":[["kibana_uuid","5b2de169-2785-441b-ae8c-186a1936b17d"],["git_rev","41883488bc4"],["myObject",{"keyA":"A","keyB":{"subKeyB":"B"}}]],"sourceValue":{"kibana_uuid":"5b2de169-2785-441b-ae8c-186a1936b17d","git_rev":"41883488bc4","myObject":{"keyA":"A","keyB":{"subKeyB":"B"}}}},"logLevel":{"source":"default","value":"info","commonName":"log_level"},"metricsInterval":{"source":"start","value":30,"sourceValue":"30s"},"serverUrl":{"source":"start","value":"https://kibana-cloud-apm.apm.us-east-1.aws.found.io/","commonName":"server_url"},"transactionSampleRate":{"source":"start","value":1,"commonName":"transaction_sample_rate"},"captureSpanStackTraces":{"source":"start","sourceValue":false},"secretToken":{"source":"start","value":"[REDACTED]","commonName":"secret_token"},"serviceName":{"source":"environment","value":"kibana","commonName":"service_name"},"serviceVersion":{"source":"start","value":"8.15.0","commonName":"service_version"}},"activationMethod":"require","message":"Elastic APM Node.js Agent v4.7.0"}

package.json dependencies:

Click to expand

"elastic-apm-node": "^4.7.0",

[afharo]

For extra context, I noticed that changing the config to

- {"kibana_uuid":"5b2de169-2785-441b-ae8c-186a1936b17d","git_rev":"41883488bc4","myObject":{"keyA":"A","keyB":{"subKeyB":"B"}}}}
+ {"kibana_uuid":"5b2de169-2785-441b-ae8c-186a1936b17d","git_rev":"592aafcaba2","myObject.keyA":"A","myObject.keyB.subKeyB":"B"}}

Solves the issue (it automatically applies the underscore conversion)