# Structured Logging A structured logging system can be useful when your logs are destined for a machine to parse and process. By maintaining its machine-readable characteristics, it enables more efficient searching and aggregations when consumed by software such as the "ELK stack". Synapse's structured logging system is configured via the file that Synapse's `log_config` config option points to. The file should include a formatter which uses the `synapse.logging.TerseJsonFormatter` class included with Synapse and a handler which uses the above formatter. There is also a `synapse.logging.JsonFormatter` option which does not include a timestamp in the resulting JSON. This is useful if the log ingester adds its own timestamp. A structured logging configuration looks similar to the following: ```yaml version: 1 formatters: structured: class: synapse.logging.TerseJsonFormatter handlers: file: class: logging.handlers.TimedRotatingFileHandler formatter: structured filename: /path/to/my/logs/homeserver.log when: midnight backupCount: 3 # Does not include the current log file. encoding: utf8 loggers: synapse: level: INFO handlers: [remote] synapse.storage.SQL: level: WARNING ``` The above logging config will set Synapse as 'INFO' logging level by default, with the SQL layer at 'WARNING', and will log to a file, stored as JSON. It is also possible to figure Synapse to log to a remote endpoint by using the `synapse.logging.RemoteHandler` class included with Synapse. It takes the following arguments: - `host`: Hostname or IP address of the log aggregator. - `port`: Numerical port to contact on the host. - `maximum_buffer`: (Optional, defaults to 1000) The maximum buffer size to allow. A remote structured logging configuration looks similar to the following: ```yaml version: 1 formatters: structured: class: synapse.logging.TerseJsonFormatter handlers: remote: class: synapse.logging.RemoteHandler formatter: structured host: 10.1.2.3 port: 9999 loggers: synapse: level: INFO handlers: [remote] synapse.storage.SQL: level: WARNING ``` The above logging config will set Synapse as 'INFO' logging level by default, with the SQL layer at 'WARNING', and will log JSON formatted messages to a remote endpoint at 10.1.2.3:9999. ## Upgrading from legacy structured logging configuration Versions of Synapse prior to v1.23.0 included a custom structured logging configuration which is deprecated. It used a `structured: true` flag and configured `drains` instead of ``handlers`` and `formatters`. Synapse currently automatically converts the old configuration to the new configuration, but this will be removed in a future version of Synapse. The following reference can be used to update your configuration. Based on the drain `type`, we can pick a new handler: 1. For a type of `console`, `console_json`, or `console_json_terse`: a handler with a class of `logging.StreamHandler` and a `stream` of `ext://sys.stdout` or `ext://sys.stderr` should be used. 2. For a type of `file` or `file_json`: a handler of `logging.FileHandler` with a location of the file path should be used. 3. For a type of `network_json_terse`: a handler of `synapse.logging.RemoteHandler` with the host and port should be used. Then based on the drain `type` we can pick a new formatter: 1. For a type of `console` or `file` no formatter is necessary. 2. For a type of `console_json` or `file_json`: a formatter of `synapse.logging.JsonFormatter` should be used. 3. For a type of `console_json_terse` or `network_json_terse`: a formatter of `synapse.logging.TerseJsonFormatter` should be used. For each new handler and formatter they should be added to the logging configuration and then assigned to either a logger or the root logger. An example legacy configuration: ```yaml structured: true loggers: synapse: level: INFO synapse.storage.SQL: level: WARNING drains: console: type: console location: stdout file: type: file_json location: homeserver.log ``` Would be converted into a new configuration: ```yaml version: 1 formatters: json: class: synapse.logging.JsonFormatter handlers: console: class: logging.StreamHandler stream: ext://sys.stdout file: class: logging.FileHandler formatter: json filename: homeserver.log loggers: synapse: level: INFO handlers: [console, file] synapse.storage.SQL: level: WARNING ``` The new logging configuration is a bit more verbose, but significantly more flexible. It allows for configuration that were not previously possible, such as sending plain logs over the network, or using different handlers for different modules.