Add the longFieldMaxLength integer configuration option (default 10000). Specific transaction/span/error fields (see the list below) will be truncated at this number of unicode characters. (#2193, #1921)

The `errorMessageMaxLength` configuration option is now *deprecated*, but
still supported. Users should switch to using `longFieldMaxLength. If
`errorMessageMaxLength` is not specified, truncation of error messages will
now use the `longFieldMaxLength` value.

Note that ultimately the maximum length of any tracing field is limited by the
{apm-server-ref-v}/configuration-process.html#max_event_size[`max_event_size`]
configured for the receiving APM server.

The fields affected by `longFieldMaxLength` are:

Performance improvements have been made in error and stacktrace capture (#2094). This also included in two bug fixes:

The handling of sending events (transactions, spans, errors) to APM server has improved in a few ways. During temporary spikes in load and/or an APM server that is unresponsive, the agent will buffer a number of events and drop them above a certain limit (configurable via maxQueueSize). This helps ensure the agent does not overly consume memory and CPU. As well, the agent will now backoff when the APM server errors. Finally, improved error handling means it will terminate failing requests to the APM server more quickly.

Note: v1 of this agent (EOL’d 2 years ago), included a maxQueueSize config variable with a different meaning. If you have a lingering usage of that setting (also possibly as the ELASTIC_APM_MAX_QUEUE_SIZE environment variable), then it should be removed.

The APM agent’s own internal logging now uses structured JSON logging using the pino API, and formatted in ecs-logging format. The log records on stdout are now single-line JSON objects. For example:

# Before
APM Server transport error (ECONNREFUSED): connect ECONNREFUSED 127.0.0.1:8200

# After
{"log.level":"error","@timestamp":"2021-03-19T00:21:17.571Z","log":{"logger":"elastic-apm-node"},
"ecs":{"version":"1.6.0"},"message":"APM Server transport error (ECONNREFUSED): connect ECONNREFUSED 127.0.0.1:8200"}

Pretty formatting (and filtering) on the console may be done via the ecslog tool.

A custom logger is still supported as before. However, a non-pino custom logger will only receive the "message" field, and not structured log fields as they are added over time.

feat: Add automatic instrumentation of the @elastic/elasticsearch package #1870

The instrumentation of the legacy "elasticsearch" package has also changed slightly to commonalize:

feat: Add sanitize_field_names configuration option.
Allows users to configure a list of wildcard patterns to remove items from the agent’s HTTP header and application/x-www-form-urlencoded payloads. #1898

fix: Fix parsing of comma-separated strings for relevant config vars to allow whitespace around the commas. E.g.:

export ELASTIC_APM_TRANSACTION_IGNORE_URLS='/ping, /metrics*'

Config vars affected are: disableInstrumentations, transactionIgnoreUrls addPatch, and globalLabels.