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

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?

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")

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