logger: alter loglevel behavior

Author: tamor1

README.md

@@ -133,8 +133,8 @@ additional details on each available environment variable.
 | `AWS_SECRET_ACCESS_KEY` | EXAMPLEKEY | The [secret key](http://docs.aws.amazon.com/general/latest/gr/aws-security-credentials.html) used by the agent for all calls. | Taken from Amazon EC2 instance metadata. | Taken from Amazon EC2 instance metadata. |
 | `AWS_SESSION_TOKEN` | | The [session token](http://docs.aws.amazon.com/STS/latest/UsingSTS/Welcome.html) used for temporary credentials. | Taken from Amazon EC2 instance metadata. | Taken from Amazon EC2 instance metadata. |
 | `DOCKER_HOST`   | `unix:///var/run/docker.sock` | Used to create a connection to the Docker daemon; behaves similarly to this environment variable as used by the Docker client. | `unix:///var/run/docker.sock` | `npipe:////./pipe/docker_engine` |
-| `ECS_LOGLEVEL`  | <crit> | <error> | <warn> | <info> | <debug> | The level of detail that should be logged by the logging driver, or on Windows, the Windows Event Log. | info | info |
-| `ECS_LOGLEVEL_ON_INSTANCE`  | <none> | <crit> | <error> | <warn> | <info> | <debug> | The level of detail that should be logged in the on-instance log file. | none if `ECS_LOG_DRIVER` is explicitly set to a non-empty value; info otherwise | none if `ECS_LOG_DRIVER` is explicitly set to a non-empty value; info otherwise |
+| `ECS_LOGLEVEL`  | <crit> | <error> | <warn> | <info> | <debug> | The level of detail to be logged. | info | info |
+| `ECS_LOGLEVEL_ON_INSTANCE`  | <none> | <crit> | <error> | <warn> | <info> | <debug> | Can be used to override `ECS_LOGLEVEL` and set a level of detail that should be logged in the on-instance log file, separate from the level that is logged in the logging driver. If a logging driver is explicitly set, on-instance logs are turned off by default, but can be turned back on with this variable. | none if `ECS_LOG_DRIVER` is explicitly set to a non-empty value; otherwise the same value as `ECS_LOGLEVEL` | none if `ECS_LOG_DRIVER` is explicitly set to a non-empty value; otherwise the same value as `ECS_LOGLEVEL` |
 | `ECS_LOGFILE`   | /ecs-agent.log              | The location where logs should be written. Log level is controlled by `ECS_LOGLEVEL`. | blank | blank |
 | `ECS_CHECKPOINT`   | <true | false> | Whether to checkpoint state to the DATADIR specified below. | true if `ECS_DATADIR` is explicitly set to a non-empty value; false otherwise | true if `ECS_DATADIR` is explicitly set to a non-empty value; false otherwise |
 | `ECS_DATADIR`      |   /data/                  | The container path where state is checkpointed for use across agent restarts. Note that on Linux, when you specify this, you will need to make sure that the Agent container has a bind mount of `$ECS_HOST_DATA_DIR/data:$ECS_DATADIR` with the corresponding values of `ECS_HOST_DATA_DIR` and `ECS_DATADIR`. | /data/ | `C:\ProgramData\Amazon\ECS\data`

agent/logger/log.go

@@ -163,6 +163,9 @@ func setInstanceLevelDefault() string {
 	if logDriver := os.Getenv(LOG_DRIVER_ENV_VAR); logDriver != "" {
 		return DEFAULT_LOGLEVEL_WHEN_DRIVER_SET
 	}
+	if loglevel := os.Getenv(LOGLEVEL_ENV_VAR); loglevel != "" {
+		return loglevel
+	}
 	return DEFAULT_LOGLEVEL
 }