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Add logging for dns lookups with timestamps #3631

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54eec9a
Add logging for dns lookups with timestamps
Tanzp01 Sep 27, 2025
65b188b
always enable errorLogger and replace the error message with errorLogger
Tanzp01 Oct 6, 2025
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34 changes: 28 additions & 6 deletions dns/dnsperfgo/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ import (
"flag"
"fmt"
"log"
"log/slog"
"net"
"net/http"
"os"
Expand All @@ -39,10 +40,10 @@ import (
const clusterDomain = "cluster.local"

type Config struct {
qps int
testDuration, idleDuration, queryTimeout time.Duration
hostnameFile string
queryClusterNames, logQueries bool
qps int
testDuration, idleDuration, queryTimeout time.Duration
hostnameFile string
queryClusterNames, logQueries, enableLatencyLogging bool
}

type dnsClient struct {
Expand All @@ -59,6 +60,13 @@ type dnsClient struct {

type LookupFunc func(string) ([]string, error)

var (
// infoLogger writes to stdout, initialized if flag is set.
infoLogger *slog.Logger
// errorLogger writes to stderr, initialized if flag is set.
errorLogger *slog.Logger
)

func main() {
config := Config{}
flag.IntVar(&config.qps, "qps", 10, "The number of DNS queries per second to issue")
Expand All @@ -68,8 +76,12 @@ func main() {
flag.StringVar(&config.hostnameFile, "inputfile", "", "Path to the file containing hostnames to lookup. Hostnames should be newline-separated.")
flag.BoolVar(&config.queryClusterNames, "query-cluster-names", false, "Indicates whether the query names should be the service names in the cluster.")
flag.BoolVar(&config.logQueries, "log-queries", false, "Indicates whether each query should be logged.")

flag.BoolVar(&config.enableLatencyLogging, "enable-latency-logging", false, "Indicate whether to enable structured logging for each DNS lookup latency.")
flag.Parse()
if config.enableLatencyLogging {
infoLogger = slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo}))
}
errorLogger = slog.New(slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
log.Printf("Starting dnstest with config parameters - %+v", config)
client := &dnsClient{config: &config, stopChan: make(chan os.Signal, 1)}
signal.Notify(client.stopChan, syscall.SIGTERM)
Expand Down Expand Up @@ -223,6 +235,12 @@ func (c *dnsClient) runQuery(name string, timeout time.Duration, lookupFunc Look
startTime := time.Now()
_, err := lookupFunc(name)
latency := time.Since(startTime)
if infoLogger != nil && err == nil {
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why not route the infoLogger to a dummy logger that doesn't output instead of having if statements?

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I also recommend logging for all lookups, irrespective of err == nil or not.

infoLogger.Info("DNS lookup successful, latency recorded",
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suggest:

infoLogger("lookup", "name", name, "latency_ms", latency.Milliseconds(), "err", err)

Latency we want in milliseconds
Record the error.

"hostname", name,
"latency_seconds", latency.Seconds(),
)
}
dnsLatency.Observe(latency.Seconds())
resultChan <- err
}(resultChan)
Expand All @@ -235,7 +253,11 @@ func (c *dnsClient) runQuery(name string, timeout time.Duration, lookupFunc Look
log.Printf("DNS lookup of name %q, err - %v\n", name, err)
}
if err != nil {
log.Printf("Failed DNS lookup of name %q, err - %v\n", name, err)
errorLogger.Error("Failed DNS lookup",
"hostname", name,
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make it easier to maintain -- "name", name

"error", err.Error(),
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Do you need to call Error? Isn't it extraneous?

"timed_out", timedOut,
)
}
c.updateResults(timedOut, err)
}()
Expand Down