Is it possible to update the log level of a zap logger at runtime?

Question

I created a logger with kubebuilder, it is based on zap logger:

import (
    "flag"
    "github.com/gin-gonic/gin"
    "net/http"
    "os"
    "go.uber.org/zap/zapcore"
    uzap "go.uber.org/zap"
    // Import all Kubernetes client auth plugins (e.g. Azure, GCP, OIDC, etc.)
    // to ensure that exec-entrypoint and run can make use of them.
    _ "k8s.io/client-go/plugin/pkg/client/auth"

    "k8s.io/apimachinery/pkg/runtime"
    utilruntime "k8s.io/apimachinery/pkg/util/runtime"
    clientgoscheme "k8s.io/client-go/kubernetes/scheme"
    ctrl "sigs.k8s.io/controller-runtime"
    "sigs.k8s.io/controller-runtime/pkg/healthz"
    "sigs.k8s.io/controller-runtime/pkg/log/zap"

)

var (
    scheme   = runtime.NewScheme()
    setupLog = ctrl.Log.WithName("setup")
)

var zapOpts []uzap.Option
    zapOpts = append(zapOpts, uzap.AddCaller())
    zapOpts = append(zapOpts, uzap.AddCallerSkip(1))
    zapOpts = append(zapOpts, uzap.AddStacktrace(uzap.DebugLevel))

    opts := zap.Options{
        Development:     developmentFlag,
        StacktraceLevel: stacktraceLevel,
        Level:           level,
        Encoder:         encoder,
        ZapOpts:  zapOpts,
    }

    opts.BindFlags(flag.CommandLine)
    flag.Parse()

    ctrl.SetLogger(zap.New(zap.UseFlagOptions(&opts)))

Now I want to change the log level to zapcore.InfoLevel at run time. I didn't find any SetLogLevel or similar API.

Do I need to create new opts and then set the new level?

Also I need to set the logger with sigs.k8s.io/controller-runtime/pkg/log/zap library. The interface of the logger is from go-logr and it implements logr.Logger interface. If I tried to change it to zapcore.NewCore than I can't set the logger with ctrl.SetLogger anymore.

I want to keep the options to update all the options of zap.Options and also to change the log level, and still to use the zap from sigs.k8s.io/controller-runtime/pkg/log/zap.

Is it possible to do it with sigs.k8s.io/controller-runtime/pkg/log/zap and sigs.k8s.io/controller-runtime?

Answer 1

Yes it is possible using AtomicLevel. From the docs:

atom := zap.NewAtomicLevel()

// To keep the example deterministic, disable timestamps in the output.
encoderCfg := zap.NewProductionEncoderConfig()
encoderCfg.TimeKey = ""

logger := zap.New(zapcore.NewCore(
    zapcore.NewJSONEncoder(encoderCfg),
    zapcore.Lock(os.Stdout),
    atom,
))
defer logger.Sync()

logger.Info("info logging enabled")
atom.SetLevel(zap.ErrorLevel)
logger.Info("info logging disabled")

Answer 2

Better answer: as suggested by @Oliver Dain, use zap.AtomicLevel. See their answer for details.

Another option is to create a core with a custom LevelEnabler function. You can use zap.LevelEnablerFunc to convert a closure to a zapcore.LevelEnabler.

The relevant docs:

LevelEnabler decides whether a given logging level is enabled when logging a message.

LevelEnablerFunc is a convenient way to implement zapcore.LevelEnabler with an anonymous function.

That function may then return true or false based on some other variable that changes at runtime:

    // will be actually initialized and changed at run time 
    // based on your business logic
    var infoEnabled bool 

    errorUnlessEnabled := zap.LevelEnablerFunc(func(level zapcore.Level) bool {
        // true: log message at this level
        // false: skip message at this level
        return level >= zapcore.ErrorLevel || infoEnabled
    })

    core := zapcore.NewCore(
        zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
        os.Stdout,
        errorUnlessEnabled,
    )
    logger := zap.New(core)

    logger.Info("foo") // not logged
    
    infoEnabled = true

    logger.Info("foo again") // logged

PS: this code is contrived. Your program will have to implement initialization, value change at run-time and proper synchronization (if needed) over the infoEnabled variable.

You can run this example in the playground: https://play.golang.org/p/oT3nvnP1Bwc