Logging Configuration¶
Source https://github.com/vllm-project/vllm/blob/main/examples/features/logging_configuration.md.
vLLM leverages Python's logging.config.dictConfig functionality to enable
robust and flexible configuration of the various loggers used by vLLM.
For vllm serve, configure logging with CLI arguments:
- Use the built-in configuration, optionally with
--log-level. - Emit structured JSON with
--logging-config.formatter json. - Use a custom Python logging configuration file with
--logging-config.pylogging_config_file. - Disable vLLM logging configuration with
--logging-config.configure_logging false.
CLI logging configuration¶
--logging-config accepts a JSON object. Its fields are log_level,
formatter, configure_logging, and pylogging_config_file. For example:
vllm serve mistralai/Mistral-7B-v0.1 \
--logging-config '{"log_level":"DEBUG","configure_logging":true}'
Fields can also be set individually with dotted arguments:
The built-in text formatter is selected by default. To emit one JSON object
per vLLM and Uvicorn log record, select the built-in json formatter:
The built-in JSON output includes asctime, levelname, name,
processName, process, message, and vllm_process_name. processName is
Python's process name, vllm_process_name identifies vLLM's logical process
(including worker ranks where applicable), and process is the
operating-system PID.
The built-in profile formats records emitted through vLLM's Python loggers and
Uvicorn's server and access loggers when using vllm serve. It does not convert
direct writes to stdout or stderr. Use a custom configuration to format
other loggers.
--log-level is a shortcut for --logging-config.log_level and takes
precedence if both are supplied. It sets the level of vLLM's built-in logging
configuration. --log-config-file is deprecated and will be removed in
v0.33.0; use --logging-config.pylogging_config_file in new commands.
If configure_logging is false, vLLM does not apply a logging
configuration. It cannot be combined with pylogging_config_file. This has
the same effect as the legacy VLLM_CONFIGURE_LOGGING=0 setting.
The custom logging configuration file must be JSON following Python's logging configuration dictionary schema.
Custom configurations override built-in formatter settings
When pylogging_config_file is set, vLLM loads that JSON file and replaces
its built-in dictConfig; it does not merge the two. Therefore, log_level
and formatter apply only when no custom configuration file is provided.
Set levels and formatters in the custom file itself. vLLM applies the
resolved configuration in its child processes as well.
Environment variables¶
The CLI configuration is recommended for vllm serve. The legacy
VLLM_CONFIGURE_LOGGING, VLLM_LOGGING_LEVEL, and
VLLM_LOGGING_CONFIG_PATH variables remain supported as defaults. The default
handler's stream, prefix, and color are currently controlled only through
environment variables. Values from a YAML --config file or the command line
override those defaults. See Environment Variables
for those settings.
Examples¶
Example 1: Customize vLLM root logger¶
For more control over fields and handlers, configure the vLLM root logger and
Uvicorn's server and access loggers with
python-json-logger
(which is part of the container image) to log to STDOUT in JSON format at
INFO level.
To begin, first, create an appropriate JSON logging configuration file:
/path/to/logging_config.json
{
"formatters": {
"json": {
"class": "pythonjsonlogger.jsonlogger.JsonFormatter",
"format": "%(asctime)s %(levelname)s %(name)s %(vllm_process_name)s %(process)d %(message)s"
}
},
"handlers": {
"console": {
"class" : "logging.StreamHandler",
"formatter": "json",
"level": "INFO",
"stream": "ext://sys.stdout"
}
},
"loggers": {
"vllm": {
"handlers": ["console"],
"level": "INFO",
"propagate": false
},
"uvicorn": {
"handlers": ["console"],
"level": "INFO",
"propagate": false
},
"uvicorn.error": {
"handlers": ["console"],
"level": "INFO",
"propagate": false
},
"uvicorn.access": {
"handlers": ["console"],
"level": "INFO",
"propagate": false
}
},
"disable_existing_loggers": false,
"version": 1
}
Finally, run vLLM with the custom logging configuration JSON file:
vllm serve mistralai/Mistral-7B-v0.1 --max-model-len 2048 \
--logging-config.pylogging_config_file /path/to/logging_config.json
With this custom configuration, each vLLM and Uvicorn log record is one JSON
object. The example selects vllm_process_name and process explicitly; both
fields are also present in the built-in JSON output described above. vLLM
avoids altering stdout or stderr, so no text is prepended to JSON log
records.
This applies to records emitted through the configured Python loggers. A JSON
formatter cannot convert unrelated output into JSON, such as a third-party
library writing directly to stdout or stderr; configure or route such
output separately when a consumer requires every collected line to be JSON.
When serving, vLLM also passes this file to Uvicorn as its logging
configuration. The uvicorn, uvicorn.error, and uvicorn.access entries
format its server and access logs as JSON.
Example 2: Silence a particular vLLM logger¶
To silence a particular vLLM logger, it is necessary to provide custom logging configuration for the target logger that configures the logger so that it won't propagate its log messages to the root vLLM logger.
When custom configuration is provided for any logger, it is also necessary to provide configuration for the root vLLM logger since any custom logger configuration overrides the built-in default logging configuration used by vLLM.
First, create an appropriate JSON logging configuration file that includes configuration for the root vLLM logger and for the logger you wish to silence:
/path/to/logging_config.json
{
"formatters": {
"vllm": {
"class": "vllm.logging_utils.NewLineFormatter",
"datefmt": "%m-%d %H:%M:%S",
"format": "%(levelname)s %(asctime)s %(filename)s:%(lineno)d] %(message)s"
}
},
"handlers": {
"vllm": {
"class" : "logging.StreamHandler",
"formatter": "vllm",
"level": "INFO",
"stream": "ext://sys.stdout"
}
},
"loggers": {
"vllm": {
"handlers": ["vllm"],
"level": "DEBUG",
"propagate": false
},
"vllm.example_noisy_logger": {
"propagate": false
}
},
"version": 1
}
Finally, run vLLM with the custom logging configuration JSON file:
vllm serve mistralai/Mistral-7B-v0.1 --max-model-len 2048 \
--logging-config.pylogging_config_file /path/to/logging_config.json
Example 3: Disable vLLM default logging configuration¶
To disable vLLM's default logging configuration and silence vLLM log output,
set --logging-config.configure_logging false when running vLLM. This prevents
vLLM from configuring the root vLLM logger, which in turn silences other vLLM
loggers unless the application or Python root logger configures a handler.
vllm serve mistralai/Mistral-7B-v0.1 --max-model-len 2048 \
--logging-config.configure_logging false
For legacy launch scripts, VLLM_CONFIGURE_LOGGING=0 has the same effect.
Example 4: Disable access logs for health check endpoints¶
In production environments, health check endpoints like /health, /metrics,
and /ping are frequently called by load balancers and monitoring systems,
generating a large volume of repetitive access logs. To reduce log noise while
keeping logs for other endpoints, use the --disable-access-log-for-endpoints
option.
Disable access logs for health and metrics endpoints:
vllm serve mistralai/Mistral-7B-v0.1 --max-model-len 2048 \
--disable-access-log-for-endpoints /health,/metrics,/ping
Common endpoints to consider filtering:
| Endpoint | Description | Typical Caller |
|---|---|---|
/health |
Health check | Kubernetes liveness/readiness probes, load balancers |
/metrics |
Prometheus metrics | Prometheus scraper (every 15-60s) |
/ping |
SageMaker health check | SageMaker infrastructure |
/load |
Server load metrics | Custom monitoring |
Notes:
- This option only affects uvicorn access logs, not vLLM application logs
- Specify multiple endpoints by separating them with commas (no spaces)
- The filter uses exact path matching, query parameters are ignored (e.g.,
/health?verbose=truematches/health) - If you need to completely disable all access logs, use
--disable-uvicorn-access-loginstead