Docker logging¶

SC4SNMP applications write logs to container standard output and standard error. Docker controls how those container logs are stored and retained. These settings do not change SC4SNMP log levels, messages, formats, or destinations.

The default Compose configuration uses the json-file driver with bounded rotation for every service:

DOCKER_LOG_DRIVER=json-file
DOCKER_LOG_MAX_SIZE=10m
DOCKER_LOG_MAX_FILE=5
DOCKER_LOG_COMPRESS=true

Docker applies logging-driver changes when containers are created. Run docker compose up -d after changing the logging configuration so Compose can recreate the affected containers.

Prerequisites¶

Running manage_logs.py requires the ruamel.yaml Python package. Install it with:

pip3 install ruamel.yaml

`manage_logs.py` flags¶

Flag	Description
`-p`, `--path_to_compose`	Absolute path to the directory containing the Docker Compose files
`--configure_default_logging`	Apply bounded `json-file` logging or Docker daemon inheritance based on `DOCKER_LOG_DRIVER`
`--use_docker_default_logging`	Remove service-level logging configuration so containers inherit the Docker daemon configuration

Choose the logging behavior¶

Check the Docker daemon’s current logging driver before a new installation or upgrade:

sudo docker info --format '{{.LoggingDriver}}'

Desired behavior	Value in `.env`	Result after running `--configure_default_logging`
Use bounded `json-file` logging	`DOCKER_LOG_DRIVER=json-file`	Compose applies `json-file` with the configured rotation limits
Keep the Docker daemon’s current driver	Use the value reported by `docker info`	Compose logging is removed and containers inherit the daemon driver
Explicitly inherit the daemon driver	`DOCKER_LOG_DRIVER=inherit`	Compose logging is removed and containers inherit the daemon driver
Use the SC4SNMP default	Leave the variable missing or empty	Compose applies bounded `json-file` logging

DOCKER_LOG_DRIVER is a selector used by manage_logs.py. It does not directly set a non-JSON driver on each service. For example, DOCKER_LOG_DRIVER=local makes containers use local only when local is the Docker daemon default.

Keep the current driver during an upgrade¶

If docker info reports local, add or update this line in .env file:

DOCKER_LOG_DRIVER=local

Use the exact value reported by docker info when preserving another driver. Before starting the upgraded deployment, run:

cd /home/ubuntu/docker_compose
python3 manage_logs.py \
  --path_to_compose /home/ubuntu/docker_compose \
  --configure_default_logging
sudo docker compose config --quiet
sudo docker compose up -d

The helper removes service-level logging for non-JSON values, allowing the upgraded containers to continue using the Docker daemon driver. If this step is skipped, new or recreated SC4SNMP containers use bounded json-file logging.

Switch to bounded `json-file`¶

To switch from any current logging driver to bounded json-file, set these values in .env:

DOCKER_LOG_DRIVER=json-file
DOCKER_LOG_MAX_SIZE=10m
DOCKER_LOG_MAX_FILE=5
DOCKER_LOG_COMPRESS=true

Apply the configuration:

cd /home/ubuntu/docker_compose
python3 manage_logs.py \
  --path_to_compose /home/ubuntu/docker_compose \
  --configure_default_logging
sudo docker compose config --quiet
sudo docker compose up -d

This changes logging only for the SC4SNMP Compose services. It does not change the Docker daemon or unrelated containers. Named MongoDB and Redis volumes are preserved by docker compose up -d. Do not use docker compose down -v for this change.

Verify the effective configuration¶

After the containers are recreated, check their logging drivers and options:

for id in $(sudo docker compose ps -q)
do
  sudo docker inspect \
    --format '{{.Name}} driver={{.HostConfig.LogConfig.Type}} options={{json .HostConfig.LogConfig.Config}}' \
    "$id"
done

Bounded logging reports driver=json-file with max-size, max-file, and compress. When daemon inheritance is selected, each container reports the daemon driver.

Restore Docker daemon inheritance directly¶

The following command removes service-level logging without reading DOCKER_LOG_DRIVER:

python3 manage_logs.py \
  --path_to_compose /home/ubuntu/docker_compose \
  --use_docker_default_logging
sudo docker compose up -d

This also removes the SC4SNMP service-level retention limits. If the daemon uses json-file without daemon-level max-size and max-file options, its container logs do not have a configured size limit. Check /etc/docker/daemon.json before selecting daemon inheritance.

To send Docker container logs to Splunk instead, see Sending logs to Splunk.