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Application Logging

Application Logging

In FxA Javascript/Typescript server-side applications, logging is emitted via mozlog which adheres to the mozlog schema format. The log messages are captured from stdout and aggregated into Google BigQuery via Stackdriver. Application exceptions are captured via Sentry and sent to our Sentry instance.

Stage and development logging is grouped under the fxa-nonprod project, while accessing the fxa-prod logs requires additional special access privileges.

Capturing Event Details

Once a mozlog instance is created, log events are captured with a dot concatenated string indicating an (ideally) unique location of the logging statement that is clear where in the code-base it was made, along with any additional fields to include.

Creating a mozlog instance can be done by instantiating the log object with a configuration object:

const logConfig = {
app: 'fxa-content-server',
fmt: 'heka',
level: 'info'
};
const log = require('mozlog')(logConfig);

It can then be used to log with:

log.error('push.sendPush', {uid, deviceId, err });

The above log event will have a jsonPayload.type set to push.sendPush, while the additional object properties will be attached as the jsonPayload.fields object.

Viewing Event Logs

Using bigquery, the logs can be retrieved from the application service that generated them by narrowing down the stdout table used and the originating service by its container name or querying the service table directly.

Container names for currently deployed services that output to stdout tables:

  • payments - FxA Payment Server
  • amplitude - FxA Amplitude Send
  • eventbroker - FxA Event Broker

As these change over time, a quick way to determine available container names can be done using a DISTINCT query (using the desired date):

SELECT DISTINCT(resource.labels.container_name)
FROM `moz-fx-fxa-nonprod-375e.fxa_stage_logs.stdout_20191204`

The bigquery console has tab-complete for table-names and SQL statements to make query generation easy.

Accessing logs from the FxA Auth Server, FxA Auth Db MySQL Service, etc. requires querying the appropriate table. Some table prefix examples from stage:

  • fxa-auth-server - moz-fx-fxa-nonprod-375e.fxa_stage_logs.docker_fxa_auth_20191205
  • fxa-auth-db-server - moz-fx-fxa-nonprod-375e.fxa_stage_logs.docker_fxa_auth_db_20191204

A full list of these tabale prefixes can be found in the bigquery console by clicking on the left side drop-down and expanding it under fxa_stage_logs (or prod). FxA services all start with docker_fxa_.