dev: Switch to leveled logging for alerts #95
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Google App Engine can ingest structured logs, which lets us use the new structured logger in the Go standard library. This configures log/slog with some fields renamed to fit Google Cloud's field name expectations. This setup also catches plain unstructured `log.Print` and `log.Printf` calls and emits them at "INFO" level.
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I tested this by putting some example logs in The extra annotations/fields only show up when the log line is expanded, but I think that's okay. The diff for adding test log linesdiff --git a/main.go b/main.go
index 40241e4..7f0c347 100644
--- a/main.go
+++ b/main.go
@@ -39,6 +39,13 @@ func main() {
},
})))
+ log.Printf("Jeremy test slog formatting: %s", "basic log")
+ slog.Debug("Jeremy test slog formatting", "jdk_level", -4)
+ slog.Info("Jeremy test slog formatting", "jdk_level", 0)
+ slog.Warn("Jeremy test slog formatting", "jdk_level", 4)
+ slog.Error("Jeremy test slog formatting", "jdk_level", 8)
+ log.Fatalln("Jeremy test slog formatting", "jdk_level", "panic")
+
ctx := context.Background()
appVersion := os.Getenv("GAE_VERSION")Screenshots
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Google Cloud supports log-based alerts, especially if we start adding interesting fields to our logs (such as severity levels). The Go standard library now provides
log/slogfor structured (and leveled) logging, so let's start using it!By default, the
slogdefault logger also handles unstructured logs and emits them at "INFO" level. That's exactly what I would have done for most of our logs anyway, so we don't immediately have to change any code we already have.But I did choose to change one place: end-of-batch has a
log.Fatalwhich is the same aslog.Info+os.Exit(1). Rather than exiting the whole process, I'd rather have it emit an error-level log and alert us. I also made it return an HTTP 500 response, so it still shows up as a failed cron job run.