Lambdas reserved environment variables
Lambda runtimes set several environment variables during initialization. The keys for these environment variables are reserved and cannot be set in your function configuration.
_HANDLER– The handler location configured on the function.
_X_AMZN_TRACE_ID– The X-Ray tracing header.
AWS_REGION– The AWS Region where the Lambda function is executed.
AWS_EXECUTION_ENV– The runtime identifier, prefixed by AWS_Lambda_—for example, AWS_Lambda_java8.
AWS_LAMBDA_FUNCTION_NAME– The name of the function.
AWS_LAMBDA_FUNCTION_MEMORY_SIZE– The amount of memory available to the function in MB.
AWS_LAMBDA_FUNCTION_VERSION– The version of the function being executed.
AWS_LAMBDA_INITIALIZATION_TYPE– The initialization type of the function, which is either on-demand or provisioned-concurrency. For information, see Configuring provisioned concurrency.
AWS_LAMBDA_LOG_STREAM_NAME– The name of the Amazon CloudWatch Logs group and stream for the function.
AWS_SESSION_TOKEN– The access keys obtained from the function's execution role.
AWS_LAMBDA_RUNTIME_API– (Custom runtime) The host and port of the runtime API.
LAMBDA_TASK_ROOT– The path to your Lambda function code.
LAMBDA_RUNTIME_DIR– The path to runtime libraries.
TZ– The environment's time zone (UTC). The execution environment uses NTP to synchronize the system clock.
More information about Lambda environment variables found here.