Default generated logger config causes "Permission denied: '/homeserver.log'" for non-root containers

Description

Using generate to create config files with the Docker image sets the value of handlers.file.filename inside the *.log.config file to /homeserver.log, causing the following error when running the container as non-root:

PermissionError: [Errno 13] Permission denied: '/homeserver.log'

Changing it to /data/homeserver.log fixes the issue since the synapse user has write access to that folder.

Unfortunately it’s not enough to disable the file log handler. Even when disabled an empty log file is initially created.

Steps to reproduce

• Create minimal config files with generate
• Run container in non-root mode

Version information

If not matrix.org:

• Version: v1.33.1

• Install method: Docker Image

• Platform: Kubernetes

Cause

The issue lies within how the log config is generated (https://github.com/matrix-org/synapse/blob/develop/synapse/config/logger.py#L171-L180):

    def generate_files(self, config, config_dir_path):
        log_config = config.get("log_config")
        if log_config and not os.path.exists(log_config):
            log_file = self.abspath("homeserver.log")
            print(
                "Generating log config file %s which will log to %s"
                % (log_config, log_file)
            )
            with open(log_config, "w") as log_config_file:
                log_config_file.write(DEFAULT_LOG_CONFIG.substitute(log_file=log_file))

which calls:

@staticmethod
    def abspath(file_path):
        return os.path.abspath(file_path) if file_path else file_path

Since the container runs start.py in /, the above resolves to /homeserver.log

[jakobkmar]

This currently breaks the installation of anyone trying to install Synapse the first time using Docker, could you please change the default to /data/homeserver.log until you have decided on a better approach?

This issue really requires a quick fix as the Synapse Docker guide currently does not work due to this problem.

[flavienbwk]

Same problem. I’ve edited the logging strategy as-is to make it work :

    filename: /data/homeserver.log