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docs(README): Add note about log levels / priorities / severities

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(kjære barn har mange navn :P)

Adds a small piece of documentation about the conversion between
journald priorities and Stackdriver severities to the README, as well
as information about how to easily emit messages at different
priorities from applications logging to journald.
This commit is contained in:
Vincent Ambo 2018-09-24 15:45:12 +02:00 committed by Vincent Ambo
parent 3b20abe0f8
commit a4084bf1e0
1 changed files with 23 additions and 5 deletions
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README.md
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@ -22,6 +22,8 @@ configuration as authentication tokens are retrieved from the
in Stackdriver in Stackdriver
* `journaldriver` can be used outside of GCP by configuring static * `journaldriver` can be used outside of GCP by configuring static
credentials credentials
* `journaldriver` will recognise journald's log priority levels and
convert them into equivalent Stackdriver log severity levels
## Usage on Google Cloud Platform ## Usage on Google Cloud Platform
@ -60,6 +62,24 @@ performed:
`journaldriver` if unset, but it is recommended to - for `journaldriver` if unset, but it is recommended to - for
example - set it to the machine hostname. 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 ## NixOS module
At Aprila we deploy all of our software using [NixOS][], including At Aprila we deploy all of our software using [NixOS][], including
@ -87,13 +107,11 @@ services.journaldriver = {
**Note**: The `journaldriver`-module is not yet included in a stable **Note**: The `journaldriver`-module is not yet included in a stable
release of NixOS, but it is available on the `unstable`-channel. release of NixOS, but it is available on the `unstable`-channel.
## Upcoming features:
* `journaldriver` will be added to [nixpkgs][] with a complementary
[NixOS][] module for easy configuration.
[Stackdriver Logging]: https://cloud.google.com/logging/ [Stackdriver Logging]: https://cloud.google.com/logging/
[metadata server]: https://cloud.google.com/compute/docs/storing-retrieving-metadata [metadata server]: https://cloud.google.com/compute/docs/storing-retrieving-metadata
[Google's documentation]: https://cloud.google.com/logging/docs/access-control [Google's documentation]: https://cloud.google.com/logging/docs/access-control
[NixOS]: https://nixos.org/ [NixOS]: https://nixos.org/
[contains a module]: https://github.com/NixOS/nixpkgs/pull/42134 [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