journaldriver ============= This is a small daemon used to forward logs from `journald` (systemd's logging service) to [Stackdriver Logging][]. Most existing log services are written in inefficient dynamic languages with error-prone "cover every use-case" configuration. This tool aims to fit a specific use-case very well, instead of covering every possible logging setup. `journaldriver` can be run on GCP-instances with no additional configuration as authentication tokens are retrieved from the [metadata server][]. ## Features * `journaldriver` persists the last forwarded position in the journal and will resume forwarding at the same position after a restart * `journaldriver` will recognise log entries in JSON format and forward them appropriately to make structured log entries available in Stackdriver * `journaldriver` can be used outside of GCP by configuring static credentials * `journaldriver` will recognise journald's log priority levels and convert them into equivalent Stackdriver log severity levels ## Usage on Google Cloud Platform `journaldriver` does not require any configuration when running on GCP instances. 1. Install `journaldriver` on the instance from which you wish to forward logs. 2. Ensure that the instance has the appropriate permissions to write to Stackdriver. Google continously changes how IAM is implemented on GCP, so you will have to refer to [Google's documentation][]. By default instances have the required permissions if Stackdriver Logging support is enabled in the project. 3. Start `journaldriver`, for example via `systemd`. ## Usage outside of Google Cloud Platform When running outside of GCP, the following extra steps need to be performed: 1. Create a Google Cloud Platform service account with the "Log Writer" role and download its private key in JSON-format. 2. When starting `journaldriver`, configure the following environment variables: * `GOOGLE_CLOUD_PROJECT`: Name of the GCP project to which logs should be written. * `GOOGLE_APPLICATION_CREDENTIALS`: Filesystem path to the JSON-file containing the service account's private key. * `LOG_STREAM`: Name of the target log stream in Stackdriver Logging. This will be automatically created if it does not yet exist. * `LOG_NAME`: Name of the target log to write to. This defaults to `journaldriver` if unset, but it is recommended to - for example - set it to the machine hostname. ## Log levels / severities / priorities `journaldriver` recognises [journald's priorities][] and converts them into [equivalent severities][] in Stackdriver. Both sets of values correspond to standard `syslog` priorities. The easiest way to emit log messages with priorites from an application is to use [priority prefixes][], which are compatible with structured log messages. For example, to emit a simple warning message (structured and unstructured): ``` $ echo '<4>{"fnord":true, "msg":"structured log (warning)"}' | systemd-cat $ echo '<4>unstructured log (warning)' | systemd-cat ``` ## NixOS module At Aprila we deploy all of our software using [NixOS][], including `journaldriver`. The NixOS package repository [contains a module][] for setting up `journaldriver`. On a GCP instance the only required option is this: ```nix services.journaldriver.enable = true; ``` When running outside of GCP, the configuration looks as follows: ```nix services.journaldriver = { enable = true; logStream = "prod-environment"; logName = "hostname"; googleCloudProject = "gcp-project-name"; applicationCredentials = keyFile; }; ``` **Note**: The `journaldriver`-module is not yet included in a stable release of NixOS, but it is available on the `unstable`-channel. [Stackdriver Logging]: https://cloud.google.com/logging/ [metadata server]: https://cloud.google.com/compute/docs/storing-retrieving-metadata [Google's documentation]: https://cloud.google.com/logging/docs/access-control [NixOS]: https://nixos.org/ [contains a module]: https://github.com/NixOS/nixpkgs/pull/42134 [journald's priorities]: http://0pointer.de/public/systemd-man/sd-daemon.html [equivalent severities]: https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#logseverity [priority prefixes]: http://0pointer.de/public/systemd-man/sd-daemon.html