userver: Changing the log level at runtime
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Changing the log level at runtime

Table of Contents

If your service has a server::handlers::LogLevel configured, then you may change the current logging level at runtime, without service restart.

‍Note that writing down the debug or trace logs can significantly affect the performance of the service. In addition to the overhead of writing down more log records, C++ debug symbols may be loaded from the disk to report stack traces. Such IO could lead to significant and unpredictable delays in task processing.

For a more granular logging server::handlers::DynamicDebugLog provides a way to enable logging per source file and line basis.

Logging specific locations

server::handlers::DynamicDebugLog provides the following REST API:

GET /service/log/dynamic-debug
PUT /service/log/dynamic-debug?location=LOCATION_FROM_GET
DELETE /service/log/dynamic-debug?location=LOCATION_FROM_GET

Note that the server::handlers::DynamicDebugLog handler lives at the separate components.server.listener-monitor address, so you have to request them using the listener-monitor credentials. See Production configs and best practices for more info on configuration and ideas on how to change the /service/log/dynamic-debug handle path.

Examples:

Get dynamic debug locations

$ curl -X GET 'http://127.0.0.1:1188/service/log/dynamic-debug'
core/include/userver/rcu/rcu.hpp:208  0
core/include/userver/rcu/rcu.hpp:217  0
core/include/userver/rcu/rcu.hpp:230  0
core/include/userver/rcu/rcu.hpp:239  0
core/include/userver/rcu/rcu.hpp:384  0
core/include/userver/rcu/rcu.hpp:456  0
core/include/userver/rcu/rcu.hpp:461  0
core/include/userver/rcu/rcu.hpp:464  0
core/src/cache/cache_config.cpp:151 0
core/src/cache/cache_config.cpp:194 0
...

Enable dynamic debug for a location

$ curl -X PUT 'http://127.0.0.1:1188/service/log/dynamic-debug?location=core/src/cache/cache_config.cpp:151'
OK
$ curl -X GET 'http://127.0.0.1:1188/service/log/dynamic-debug'
core/include/userver/rcu/rcu.hpp:208  0
core/include/userver/rcu/rcu.hpp:217  0
core/include/userver/rcu/rcu.hpp:230  0
core/include/userver/rcu/rcu.hpp:239  0
core/include/userver/rcu/rcu.hpp:384  0
core/include/userver/rcu/rcu.hpp:456  0
core/include/userver/rcu/rcu.hpp:461  0
core/include/userver/rcu/rcu.hpp:464  0
core/src/cache/cache_config.cpp:151 1
core/src/cache/cache_config.cpp:194 0
...

Enable dynamic debug for a whole file

$ curl -X PUT 'http://127.0.0.1:1188/service/log/dynamic-debug?location=core/src/cache/cache_config.cpp'
OK
$ curl -X GET 'http://127.0.0.1:1188/service/log/dynamic-debug'
core/include/userver/rcu/rcu.hpp:208  0
core/include/userver/rcu/rcu.hpp:217  0
core/include/userver/rcu/rcu.hpp:230  0
core/include/userver/rcu/rcu.hpp:239  0
core/include/userver/rcu/rcu.hpp:384  0
core/include/userver/rcu/rcu.hpp:456  0
core/include/userver/rcu/rcu.hpp:461  0
core/include/userver/rcu/rcu.hpp:464  0
core/src/cache/cache_config.cpp:151 1
core/src/cache/cache_config.cpp:194 1
...

Remove dynamic debug for a whole file

$ curl -X PUT 'http://127.0.0.1:1188/service/log/dynamic-debug?location=core/include/userver/rcu/rcu.hpp'
OK
$ curl -X GET 'http://127.0.0.1:1188/service/log/dynamic-debug'
core/include/userver/rcu/rcu.hpp:208  1
core/include/userver/rcu/rcu.hpp:217  1
core/include/userver/rcu/rcu.hpp:230  1
core/include/userver/rcu/rcu.hpp:239  1
core/include/userver/rcu/rcu.hpp:384  1
core/include/userver/rcu/rcu.hpp:456  1
core/include/userver/rcu/rcu.hpp:461  1
core/include/userver/rcu/rcu.hpp:464  1
core/src/cache/cache_config.cpp:151 0
core/src/cache/cache_config.cpp:194 0
...
$ curl -X DELETE 'http://127.0.0.1:1188/service/log/dynamic-debug?location=core/include/userver/rcu/rcu.hpp'
OK
$ curl -X GET 'http://127.0.0.1:1188/service/log/dynamic-debug'
core/include/userver/rcu/rcu.hpp:208  0
core/include/userver/rcu/rcu.hpp:217  0
core/include/userver/rcu/rcu.hpp:230  0
core/include/userver/rcu/rcu.hpp:239  0
core/include/userver/rcu/rcu.hpp:384  0
core/include/userver/rcu/rcu.hpp:456  0
core/include/userver/rcu/rcu.hpp:461  0
core/include/userver/rcu/rcu.hpp:464  0
core/src/cache/cache_config.cpp:151 0
core/src/cache/cache_config.cpp:194 0
...

Commands for default logger

server::handlers::LogLevel provides the following REST API:

GET /service/log-level/
PUT /service/log-level/{level} (possible values {level}: trace, debug, info, warning, error, critical, none)
PUT /service/log-level/reset

Note that the server::handlers::LogLevel handler lives at the separate components.server.listener-monitor address, so you have to request them using the listener-monitor credentials. See Production configs and best practices for more info on configuration and ideas on how to change the /service/log-level/ handle path.

Examples:

Get the current log-level

Note that / is important at the end, without it you may get a response from other handler.

$ curl 'http://127.0.0.1:1188/service/log-level/'
{"current-log-level":"info","init-log-level":"info"}

Set log-level to debug

$ curl -X PUT 'http://127.0.0.1:1188/service/log-level/debug'
{"current-log-level":"debug","init-log-level":"info"}

Restore the default log-level

$ curl -X PUT 'http://127.0.0.1:1188/service/log-level/reset'
{"current-log-level":"info","init-log-level":"info"}

Commands for custom loggers

GET /service/log-level/?logger={logger}
PUT /service/log-level/{level}?logger={logger} (possible values {level}: trace, debug, info, warning, error, critical, none)
PUT /service/log-level/reset?logger={logger}

Note that the server::handlers::LogLevel handler lives at the separate components.server.listener-monitor address, so you have to request them using the listener-monitor credentials. See Production configs and best practices for more info on configuration.

Examples:

Get the current log-level of the access logger

$ curl 'http://127.0.0.1:1188/service/log-level/?logger=access' 
{"init-log-level":"info","current-log-level":"info"}

Set the log level of the access logger to debug

$ curl 'http://127.0.0.1:1188/service/log-level/debug?logger=access' -X PUT
{"init-log-level":"info","current-log-level":"debug"}

Reset the current log level of the access logger

$ curl 'http://127.0.0.1:1188/service/log-level/reset?logger=access' -X PUT
{"init-log-level":"info","current-log-level":"info"}