"elasticApm.isStarted is not a function" crash while using @elastic/ecs-pino-format from elastic-apm-node

[trentm]

During the process of moving the Elastic APM agent over to using pino and this @elastic/ecs-pino-format package, we hit this crash:

/app/node_modules/@elastic/ecs-pino-format/index.js:55
  const apm = elasticApm && elasticApm.isStarted() ? elasticApm : null
                                       ^

TypeError: elasticApm.isStarted is not a function
    at createEcsPinoOptions (/app/node_modules/@elastic/ecs-pino-format/index.js:55:40)
    at Object.createLogger (/app/node_modules/elastic-apm-node/lib/logging.js:143:8)
    at new Config (/app/node_modules/elastic-apm-node/lib/config.js:243:27)
    at config (/app/node_modules/elastic-apm-node/lib/config.js:213:10)
    at Agent._config (/app/node_modules/elastic-apm-node/lib/agent.js:133:16)
    at new Agent (/app/node_modules/elastic-apm-node/lib/agent.js:39:8)
    at Object.<anonymous> (/app/node_modules/elastic-apm-node/index.js:5:18)
    at Module._compile (internal/modules/cjs/loader.js:1138:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1158:10)
    at Module.load (internal/modules/cjs/loader.js:986:32)

The reason is that the guarded import of the apm agent:

try {
  elasticApm = require('elastic-apm-node')
} catch (ex) {
  // Silently ignore.
}

results in elasticApm === {}, because this check is done before "elastic-apm-node" is loaded: require.cache includes:

  '/app/node_modules/elastic-apm-node/lib/agent.js': Module {
    id: '/app/node_modules/elastic-apm-node/lib/agent.js',
    path: '/app/node_modules/elastic-apm-node/lib',
    exports: {},
    parent: Module {
      id: '/app/node_modules/elastic-apm-node/index.js',
      path: '/app/node_modules/elastic-apm-node',
      exports: {},
      parent: [Module],
      filename: '/app/node_modules/elastic-apm-node/index.js',
      loaded: false,
      children: [Array],
      paths: [Array]
    },
    filename: '/app/node_modules/elastic-apm-node/lib/agent.js',
    loaded: false,
    children: [ [Module], [Module], [Module], [Module], [Module] ],
    paths: [
      '/app/node_modules/elastic-apm-node/lib/node_modules',
      '/app/node_modules/elastic-apm-node/node_modules',
      '/app/node_modules',
      '/node_modules'
    ]
  },

Note loaded: false and hence exports: {}.

This should be a situation that can only be hit if the elastic APM agent itself (or one the deps that it loads) uses ecs-pino-format. I'd like to fix this with two changes:

1. improve that guard to handle the loaded: false case
2. provide a config option to explicitly disable the APM integration with ecs-pino-format usage. I'll do this part in a separate PR. -> feat: add 'apmIntegration: false' option to disable Elastic APM integration #62