How would someone go about implementing this?

From what I can see the metadata itself will need to be added to

Lines 239 to 249 in cde2dde

    
           // metadata 
        
           agentName: 'nodejs', 
        
           agentVersion: version, 
        
           serviceName: conf.serviceName, 
        
           serviceNodeName: conf.serviceNodeName, 
        
           serviceVersion: conf.serviceVersion, 
        
           frameworkName: conf.frameworkName, 
        
           frameworkVersion: conf.frameworkVersion, 
        
           globalLabels: maybePairsToObject(conf.globalLabels), 
        
           hostname: conf.hostname, 
        
           environment: conf.environment,

(which means adding it to the apm-nodejs-http-client package)

net.createConnection() is probably the fastest way to check if the metadata server exists, if it does a request can be made to retrieve the information. This is basically what was done on the reference implementation: https://github.com/basepi/apm-agent-python/blob/f13110156e57eec99134a7f9342243416b969698/elasticapm/utils/cloud.py#L79-L115

But the biggest "issue" so far, is that the config generation is synchronous.

A possible solution to the above that does not require a big refactor would be to create the "cloud metadata fetcher" as a function that accepts a callback and then pass that to ElasticAPMHttpClient. Writing to the stream could then be deferred until the callback has been called: https://github.com/elastic/apm-nodejs-http-client/blob/1526dedc26392bd92f20b5079f848c7e77567e7c/index.js#L496-L500

Something like:

    // All requests to the APM Server must start with a metadata object
    const encodeMetadataAndWriteStream = () => {
      if (!client._encodedMetadata) {
        client._encodedMetadata = client._encode({ metadata: client._conf.metadata }, Client.encoding.METADATA)
      }

      stream.write(client._encodedMetadata)
    }

    const { metadata } = client._conf

    if (metadata._cloudFetcher && !metadata.cloud) {
      metadata._cloudFetcher((cloud, _error) => {
        // do something with error?
        metadata.cloud = cloud
        encodeMetadataAndWriteStream()
      })
    } else {
      encodeMetadataAndWriteStream()
    }

	// metadata
	agentName: 'nodejs',
	agentVersion: version,
	serviceName: conf.serviceName,
	serviceNodeName: conf.serviceNodeName,
	serviceVersion: conf.serviceVersion,
	frameworkName: conf.frameworkName,
	frameworkVersion: conf.frameworkVersion,
	globalLabels: maybePairsToObject(conf.globalLabels),
	hostname: conf.hostname,
	environment: conf.environment,

Collect cloud metadata #1815

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