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feat: support for file based live configuration reloading
A new optional flag (long: --watch-dir, short: -w) has been
added. When present any files with a ".env" suffix will be
loaded into the environment before the *GlobalConfiguration
is created, otherwise existing behavior is preserved.
In addition when the watch-dir flag is present a goroutine
will be started in serve_cmd.go and begin blocking on a call
to (*Reloader).Watch with a callback function that accepts a
*conf.GlobalConfiguration object. Each time this function is
called we create a new API object and store it within our
AtomicHandler, previously given as the root handler to the
*http.Server.
The Reloader uses some simple heuristics to deal with a few
edge cases, an overview:
- At most 1 configuration reload may happen per 10 seconds
with a +-1s margin of error.
- After a file within -watch-dir has changed the 10 second
grace period begins. After that it will reload the config.
- Config reloads first sort each file by name then processes
them in sequence.
- Directories within watch-dir are ignored during config
reloading.
- Implementation quirk: directory changes can trigger
a config reload, as I don't stat fsnotify events. This
and similar superfulous reloads could be easily fixed
by storing a snapshot of os.Environ() after successful
reloads to compare with the latest via slices.Equal()
before reloading.
- Files that do not end with a .env suffix are ignored.
- It handles the removal or renaming of the -watch-dir
during runtime, but an error message will be printed
every 10 seconds as long as it's missing.
- The config file passed with -c is only loaded once. Live
reloads only read the config dir. Meaning it would be
possible to create a config dir change that results in a
new final configuration on the next reload due to the
persistence of os.Environ().- Loading branch information
Chris Stockton
committed
Sep 10, 2024
1 parent
428d0f0
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,141 @@ | ||
| // Package reloader provides support for live configuration reloading. | ||
| package reloader | ||
|
|
||
| import ( | ||
| "context" | ||
| "log" | ||
| "strings" | ||
| "time" | ||
|
|
||
| "github.com/fsnotify/fsnotify" | ||
| "github.com/sirupsen/logrus" | ||
| "github.com/supabase/auth/internal/conf" | ||
| ) | ||
|
|
||
| const ( | ||
| // reloadInterval is the interval between configuration reloading. At most | ||
| // one configuration change may be made between this duration. | ||
| reloadInterval = time.Second * 10 | ||
|
|
||
| // tickerInterval is the maximum latency between configuration reloads. | ||
| tickerInterval = reloadInterval / 10 | ||
| ) | ||
|
|
||
| type ConfigFunc func(*conf.GlobalConfiguration) | ||
|
|
||
| type Reloader struct { | ||
| watchDir string | ||
| reloadIval time.Duration | ||
| tickerIval time.Duration | ||
| } | ||
|
|
||
| func NewReloader(watchDir string) *Reloader { | ||
| return &Reloader{ | ||
| watchDir: watchDir, | ||
| reloadIval: reloadInterval, | ||
| tickerIval: tickerInterval, | ||
| } | ||
| } | ||
|
|
||
| // reload attempts to create a new *conf.GlobalConfiguration after loading the | ||
| // currently configured watchDir. | ||
| func (rl *Reloader) reload() (*conf.GlobalConfiguration, error) { | ||
| if err := conf.LoadDirectory(rl.watchDir); err != nil { | ||
| return nil, err | ||
| } | ||
|
|
||
| cfg, err := conf.LoadGlobalFromEnv() | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| return cfg, nil | ||
| } | ||
|
|
||
| // reloadCheckAt checks if reloadConfig should be called, returns true if config | ||
| // should be reloaded or false otherwise. | ||
| func (rl *Reloader) reloadCheckAt(at, lastUpdate time.Time) bool { | ||
| if lastUpdate.IsZero() { | ||
| return false // no pending updates | ||
| } | ||
| if at.Sub(lastUpdate) < rl.reloadIval { | ||
| return false // waiting for reload interval | ||
| } | ||
|
|
||
| // Update is pending. | ||
| return true | ||
| } | ||
|
|
||
| func (rl *Reloader) Watch(ctx context.Context, fn ConfigFunc) error { | ||
| wr, err := fsnotify.NewWatcher() | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| defer wr.Close() | ||
|
|
||
| tr := time.NewTicker(rl.tickerIval) | ||
| defer tr.Stop() | ||
|
|
||
| // Ignore errors, if watch dir doesn't exist we can add it later. | ||
| if err := wr.Add(rl.watchDir); err != nil { | ||
| logrus.WithError(err).Error("watch dir failed") | ||
| } | ||
|
|
||
| var lastUpdate time.Time | ||
| for { | ||
| select { | ||
| case <-ctx.Done(): | ||
| return ctx.Err() | ||
|
|
||
| case <-tr.C: | ||
| // This is a simple way to solve watch dir being added later or | ||
| // being moved and then recreated. I've tested all of these basic | ||
| // scenarios and wr.WatchList() does not grow which aligns with | ||
| // the documented behavior. | ||
| if err := wr.Add(rl.watchDir); err != nil { | ||
| logrus.WithError(err).Error("watch dir failed") | ||
| } | ||
|
|
||
| // Check to see if the config is ready to be relaoded. | ||
| if !rl.reloadCheckAt(time.Now(), lastUpdate) { | ||
| continue | ||
| } | ||
|
|
||
| // Reset the last update time before we try to reload the config. | ||
| lastUpdate = time.Time{} | ||
|
|
||
| cfg, err := rl.reload() | ||
| if err != nil { | ||
| logrus.WithError(err).Error("config reload failed") | ||
| continue | ||
| } | ||
|
|
||
| // Call the callback function with the latest cfg. | ||
| fn(cfg) | ||
|
|
||
| case evt, ok := <-wr.Events: | ||
| if !ok { | ||
| logrus.WithError(err).Error("fsnotify has exited") | ||
| return nil | ||
| } | ||
|
|
||
| // We only read files ending in .env | ||
| if !strings.HasSuffix(evt.Name, ".env") { | ||
| continue | ||
| } | ||
|
|
||
| switch { | ||
| case evt.Op.Has(fsnotify.Create), | ||
| evt.Op.Has(fsnotify.Remove), | ||
| evt.Op.Has(fsnotify.Rename), | ||
| evt.Op.Has(fsnotify.Write): | ||
| lastUpdate = time.Now() | ||
| } | ||
| case err, ok := <-wr.Errors: | ||
| if !ok { | ||
| logrus.Error("fsnotify has exited") | ||
| return nil | ||
| } | ||
| logrus.WithError(err).Error("fsnotify has reported an error") | ||
| } | ||
| } | ||
| } |
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