feat: add runner health admission checks (#1090)

Opt-in local task-admission checks under a `health_check` config section (disabled by default):

- pause new task fetching when free disk space on the workspace volume is below the configured minimum
- optional executable health-check script — a non-zero exit, timeout, or start failure marks the runner unavailable
- checks run only while the runner is idle; the last result is reused while a job is active, and polling resumes automatically on recovery
- `/readyz` reports task-admission readiness (reusing the poll loop's last check); `/healthz` stays a process-liveness endpoint

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1090
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>

internal/app/cmd/daemon.go

@@ -147,17 +147,19 @@ func runDaemon(ctx context.Context, daemArgs *daemonArgs, configFile *string) fu
 		}
 		runner.SetCapabilitiesFromDeclare(resp)
 
+		poller := poll.New(cfg, cli, runner)
+
 		if cfg.Metrics.Enabled {
 			metrics.Init()
 			metrics.RunnerInfo.WithLabelValues(ver.Version(), resp.Msg.Runner.Name).Set(1)
 			metrics.RunnerCapacity.Set(float64(cfg.Runner.Capacity))
 			metrics.RegisterUptimeFunc(time.Now())
 			metrics.RegisterRunningJobsFunc(runner.RunningCount, cfg.Runner.Capacity)
-			metrics.StartServer(ctx, cfg.Metrics.Addr)
+			metrics.StartServer(ctx, cfg.Metrics.Addr, func() (bool, string) {
+				return poller.Ready(cfg.Metrics.ReadinessGrace)
+			})
 		}
 
-		poller := poll.New(cfg, cli, runner)
-
 		if daemArgs.Once || reg.Ephemeral {
 			done := make(chan struct{})
 			go func() {

internal/app/poll/poller.go

@@ -32,6 +32,12 @@ type IdleRunner interface {
 	OnIdle(ctx context.Context)
 }
 
+// AvailabilityRunner can temporarily pause task fetching for local resource
+// conditions such as low disk space without changing server-side scheduling.
+type AvailabilityRunner interface {
+	CanAcceptTask(ctx context.Context) (bool, string)
+}
+
 type Poller struct {
 	client       client.Client
 	runner       TaskRunner
@@ -49,6 +55,11 @@ type Poller struct {
 	// unregistered is set when the server rejects the runner with an
 	// Unauthenticated response, meaning the runner is no longer registered.
 	unregistered       atomic.Bool
+	lastHealthyPoll    atomic.Int64
+	lastPollFailed     atomic.Bool
+	availabilityMu     sync.Mutex
+	availabilityReady  bool
+	availabilityReason string
 }
 
 // workerState holds the single poller's backoff state. Consecutive empty or
@@ -70,7 +81,7 @@ func New(cfg *config.Config, client client.Client, runner TaskRunner) *Poller {
 
 	done := make(chan struct{})
 
-	return &Poller{
+	p := &Poller{
 		client: client,
 		runner: runner,
 		cfg:    cfg,
@@ -83,6 +94,10 @@ func New(cfg *config.Config, client client.Client, runner TaskRunner) *Poller {
 
 		done: done,
 	}
+	p.lastHealthyPoll.Store(time.Now().UnixNano())
+	p.availabilityReady = true
+	p.availabilityReason = "ok"
+	return p
 }
 
 func (p *Poller) Poll() {
@@ -102,6 +117,17 @@ func (p *Poller) Poll() {
 			return
 		}
 
+		ready, reason := p.localAvailability(p.pollingCtx)
+		p.reportAvailability(ready, reason)
+		if !ready {
+			p.runIdleMaintenance()
+			<-sem
+			if !p.waitBackoff(s) {
+				return
+			}
+			continue
+		}
+
 		task, ok := p.fetchTask(p.pollingCtx, s)
 		if !ok {
 			p.runIdleMaintenance()
@@ -127,6 +153,15 @@ func (p *Poller) PollOnce() {
 	defer close(p.done)
 	s := &workerState{}
 	for {
+		ready, reason := p.localAvailability(p.pollingCtx)
+		p.reportAvailability(ready, reason)
+		if !ready {
+			p.runIdleMaintenance()
+			if !p.waitBackoff(s) {
+				return
+			}
+			continue
+		}
 		task, ok := p.fetchTask(p.pollingCtx, s)
 		if !ok {
 			p.runIdleMaintenance()
@@ -154,6 +189,48 @@ func (p *Poller) Unregistered() bool {
 	return p.unregistered.Load()
 }
 
+// Ready reports whether the daemon can currently communicate with Gitea and
+// accept work, reusing the availability the poll loop last observed rather than
+// re-running the check. Transient transport failures are tolerated for grace.
+func (p *Poller) Ready(grace time.Duration) (bool, string) {
+	if p.unregistered.Load() {
+		return false, "runner is no longer registered"
+	}
+	p.availabilityMu.Lock()
+	ready, reason := p.availabilityReady, p.availabilityReason
+	p.availabilityMu.Unlock()
+	if !ready {
+		return false, reason
+	}
+	if !p.lastPollFailed.Load() {
+		return true, "ok"
+	}
+	if time.Since(time.Unix(0, p.lastHealthyPoll.Load())) <= grace {
+		return true, "polling errors within grace period"
+	}
+	return false, "unable to poll Gitea"
+}
+
+func (p *Poller) localAvailability(ctx context.Context) (bool, string) {
+	if available, ok := p.runner.(AvailabilityRunner); ok {
+		return available.CanAcceptTask(ctx)
+	}
+	return true, "ok"
+}
+
+func (p *Poller) reportAvailability(ready bool, reason string) {
+	p.availabilityMu.Lock()
+	defer p.availabilityMu.Unlock()
+	switch {
+	case !ready && p.availabilityReady:
+		log.Warnf("runner temporarily unavailable: %s", reason)
+	case ready && !p.availabilityReady:
+		log.Info("runner local health recovered, resuming task polling")
+	}
+	p.availabilityReady = ready
+	p.availabilityReason = reason
+}
+
 func (p *Poller) runIdleMaintenance() {
 	if idleRunner, ok := p.runner.(IdleRunner); ok {
 		idleRunner.OnIdle(p.jobsCtx)
@@ -273,6 +350,7 @@ func (p *Poller) fetchTask(ctx context.Context, s *workerState) (*runnerv1.Task,
 	// found no work within FetchTimeout. Treat it as an empty response and do
 	// not record the duration — the timeout value would swamp the histogram.
 	if errors.Is(err, context.DeadlineExceeded) {
+		p.markHealthyPoll()
 		s.consecutiveEmpty++
 		s.consecutiveErrors = 0 // timeout is a healthy idle response
 		metrics.PollFetchTotal.WithLabelValues(metrics.LabelResultEmpty).Inc()
@@ -291,11 +369,13 @@ func (p *Poller) fetchTask(ctx context.Context, s *workerState) (*runnerv1.Task,
 			return nil, false
 		}
 		log.WithError(err).Error("failed to fetch task")
+		p.lastPollFailed.Store(true)
 		s.consecutiveErrors++
 		metrics.PollFetchTotal.WithLabelValues(metrics.LabelResultError).Inc()
 		metrics.ClientErrors.WithLabelValues(metrics.LabelMethodFetchTask).Inc()
 		return nil, false
 	}
+	p.markHealthyPoll()
 
 	// Successful response — reset error counter.
 	s.consecutiveErrors = 0
@@ -322,3 +402,8 @@ func (p *Poller) fetchTask(ctx context.Context, s *workerState) (*runnerv1.Task,
 	metrics.PollFetchTotal.WithLabelValues(metrics.LabelResultTask).Inc()
 	return resp.Msg.Task, true
 }
+
+func (p *Poller) markHealthyPoll() {
+	p.lastHealthyPoll.Store(time.Now().UnixNano())
+	p.lastPollFailed.Store(false)
+}

internal/app/poll/poller_test.go

@@ -159,6 +159,81 @@ type idleAwareRunner struct {
 	idleCalls atomic.Int64
 }
 
+type availabilityRunner struct {
+	mockRunner
+	ready  atomic.Bool
+	reason string
+}
+
+func (r *availabilityRunner) CanAcceptTask(_ context.Context) (bool, string) {
+	if r.ready.Load() {
+		return true, "ok"
+	}
+	return false, r.reason
+}
+
+func TestPollerReady(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	poller := New(cfg, nil, &availabilityRunner{})
+
+	// /readyz reuses the availability the poll loop last recorded.
+	ready, reason := poller.Ready(time.Second)
+	assert.True(t, ready)
+	assert.Equal(t, "ok", reason)
+
+	poller.reportAvailability(false, "low disk space")
+	ready, reason = poller.Ready(time.Second)
+	assert.False(t, ready)
+	assert.Equal(t, "low disk space", reason)
+
+	poller.reportAvailability(true, "ok")
+	poller.lastPollFailed.Store(true)
+	poller.lastHealthyPoll.Store(time.Now().UnixNano())
+	ready, _ = poller.Ready(time.Second)
+	assert.True(t, ready, "transient polling errors should remain ready during grace")
+
+	poller.lastHealthyPoll.Store(time.Now().Add(-2 * time.Second).UnixNano())
+	ready, reason = poller.Ready(time.Second)
+	assert.False(t, ready)
+	assert.Equal(t, "unable to poll Gitea", reason)
+
+	poller.unregistered.Store(true)
+	ready, reason = poller.Ready(time.Second)
+	assert.False(t, ready)
+	assert.Equal(t, "runner is no longer registered", reason)
+}
+
+func TestPollerPausesAndResumesForLocalAvailability(t *testing.T) {
+	var fetches atomic.Int64
+	cli := mocks.NewClient(t)
+	cli.On("FetchTask", mock.Anything, mock.Anything).Maybe().Run(func(mock.Arguments) {
+		fetches.Add(1)
+	}).Return(connect_go.NewResponse(&runnerv1.FetchTaskResponse{}), nil)
+
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.Runner.FetchInterval = 10 * time.Millisecond
+	cfg.Runner.FetchIntervalMax = 10 * time.Millisecond
+	runner := &availabilityRunner{reason: "low disk space"}
+	poller := New(cfg, cli, runner)
+
+	var wg sync.WaitGroup
+	wg.Go(poller.Poll)
+	time.Sleep(40 * time.Millisecond)
+	assert.Zero(t, fetches.Load(), "an unavailable runner must not fetch a task")
+
+	runner.ready.Store(true)
+	require.Eventually(t, func() bool {
+		return fetches.Load() > 0
+	}, time.Second, 10*time.Millisecond, "polling should resume after local recovery")
+
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	require.NoError(t, poller.Shutdown(shutdownCtx))
+	wg.Wait()
+}
+
 func (m *mockRunner) Run(ctx context.Context, _ *runnerv1.Task) error {
 	atomicMax(&m.maxConcurrent, m.running.Add(1))
 	select {

internal/app/run/disk_other.go

@@ -0,0 +1,12 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !aix && !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !solaris && !windows
+
+package run
+
+import "fmt"
+
+func freeDiskBytes(path string) (uint64, error) {
+	return 0, fmt.Errorf("free disk space checks are not supported for %s", path)
+}

internal/app/run/disk_test.go

@@ -0,0 +1,53 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package run
+
+import (
+	"testing"
+
+	"gitea.com/gitea/runner/internal/pkg/config"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCanAcceptTaskDiskGuard(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.Host.WorkdirParent = t.TempDir()
+	cfg.HealthCheck.Enabled = true
+	r := &Runner{cfg: cfg}
+
+	ready, _ := r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+
+	cfg.HealthCheck.MinFreeDiskSpaceMB = 1 << 40
+	ready, reason := r.CanAcceptTask(t.Context())
+	assert.False(t, ready)
+	assert.Contains(t, reason, "low disk space")
+}
+
+func TestDiskCheckDeferredWhileJobRuns(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.HealthCheck.Enabled = true
+	cfg.HealthCheck.MinFreeDiskSpaceMB = 1
+	cfg.Host.WorkdirParent = t.TempDir()
+	r := &Runner{cfg: cfg}
+
+	ready, reason := r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+	assert.Equal(t, "ok", reason)
+
+	cfg.HealthCheck.MinFreeDiskSpaceMB = 1 << 40
+	r.runningCount.Store(1)
+	ready, reason = r.CanAcceptTask(t.Context())
+	assert.True(t, ready, "the disk check must not run while a job is active")
+	assert.Equal(t, "ok", reason)
+
+	r.runningCount.Store(0)
+	ready, reason = r.CanAcceptTask(t.Context())
+	assert.False(t, ready)
+	assert.Contains(t, reason, "low disk space")
+}

internal/app/run/disk_unix.go

@@ -0,0 +1,16 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+
+package run
+
+import "golang.org/x/sys/unix"
+
+func freeDiskBytes(path string) (uint64, error) {
+	var stat unix.Statfs_t
+	if err := unix.Statfs(path, &stat); err != nil {
+		return 0, err
+	}
+	return stat.Bavail * uint64(stat.Bsize), nil
+}

internal/app/run/disk_windows.go

@@ -0,0 +1,20 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build windows
+
+package run
+
+import "golang.org/x/sys/windows"
+
+func freeDiskBytes(path string) (uint64, error) {
+	pathPtr, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		return 0, err
+	}
+	var available uint64
+	if err := windows.GetDiskFreeSpaceEx(pathPtr, &available, nil, nil); err != nil {
+		return 0, err
+	}
+	return available, nil
+}

internal/app/run/health_check.go

@@ -0,0 +1,106 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package run
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"maps"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"time"
+
+	"gitea.com/gitea/runner/act/common"
+	"gitea.com/gitea/runner/internal/pkg/process"
+)
+
+func (r *Runner) checkConfiguredHealth(ctx context.Context) (bool, string) {
+	script := r.cfg.HealthCheck.Script
+	if script == "" {
+		return true, "ok"
+	}
+
+	now := time.Now()
+	if r.now != nil {
+		now = r.now()
+	}
+	if !r.healthCheckLast.IsZero() && now.Sub(r.healthCheckLast) < r.cfg.HealthCheck.Interval {
+		return r.healthCheckReady, r.healthCheckReason
+	}
+
+	env := processEnvironment()
+	maps.Copy(env, r.cloneEnvs())
+	env["GITEA_RUNNER_HEALTH_CHECK"] = "true"
+	env["GITEA_RUNNER_NAME"] = r.name
+	if r.client != nil {
+		env["GITEA_INSTANCE_URL"] = r.client.Address()
+	}
+	env["GITEA_RUNNER_RUNNING_JOBS"] = strconv.FormatInt(r.RunningCount(), 10)
+
+	runner := r.runHealthCheck
+	if runner == nil {
+		runner = executeHealthCheck
+	}
+	err := runner(ctx, script, r.cfg.HealthCheck.Timeout, env)
+	r.healthCheckLast = now
+	r.healthCheckReady = err == nil
+	if err != nil {
+		r.healthCheckReason = "runner health check failed: " + err.Error()
+	} else {
+		r.healthCheckReason = "ok"
+	}
+	return r.healthCheckReady, r.healthCheckReason
+}
+
+func executeHealthCheck(ctx context.Context, script string, timeout time.Duration, env map[string]string) error {
+	checkCtx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	cmd := exec.CommandContext(checkCtx, script)
+	cmd.Env = envListFromMap(env)
+	cmd.SysProcAttr = process.SysProcAttr(script, false)
+	writer := common.NewLineWriter(func(line string) bool {
+		line = strings.TrimRight(line, "\r\n")
+		if line != "" {
+			common.Logger(ctx).Infof("health check: %s", line)
+		}
+		return true
+	})
+	cmd.Stdout = writer
+	cmd.Stderr = writer
+
+	treeKill := process.NewTreeKill(cmd)
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("start: %w", err)
+	}
+	if killer, err := treeKill.Capture(cmd.Process); err == nil {
+		defer killer.Close()
+	}
+	err := cmd.Wait()
+	common.FlushWriter(writer)
+	if errors.Is(checkCtx.Err(), context.DeadlineExceeded) {
+		return fmt.Errorf("timed out after %s", timeout)
+	}
+	if err == nil {
+		return nil
+	}
+	var exitErr *exec.ExitError
+	if errors.As(err, &exitErr) {
+		return fmt.Errorf("exited with code %d", exitErr.ExitCode())
+	}
+	return err
+}
+
+func processEnvironment() map[string]string {
+	environ := os.Environ()
+	env := make(map[string]string, len(environ))
+	for _, value := range environ {
+		if key, item, ok := strings.Cut(value, "="); ok {
+			env[key] = item
+		}
+	}
+	return env
+}

internal/app/run/health_check_test.go

@@ -0,0 +1,148 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package run
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"gitea.com/gitea/runner/internal/pkg/config"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestConfiguredHealthCheckCachesAndRecovers(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.HealthCheck.Enabled = true
+	cfg.HealthCheck.Script = "/health-check"
+	cfg.HealthCheck.Interval = time.Minute
+	cfg.HealthCheck.Timeout = time.Second
+
+	now := time.Now()
+	calls := 0
+	fail := true
+	r := &Runner{
+		cfg:  cfg,
+		name: "runner-1",
+		now:  func() time.Time { return now },
+		runHealthCheck: func(_ context.Context, script string, timeout time.Duration, env map[string]string) error {
+			calls++
+			assert.Equal(t, "/health-check", script)
+			assert.Equal(t, time.Second, timeout)
+			assert.Equal(t, "true", env["GITEA_RUNNER_HEALTH_CHECK"])
+			assert.Equal(t, "runner-1", env["GITEA_RUNNER_NAME"])
+			if fail {
+				return errors.New("unhealthy")
+			}
+			return nil
+		},
+	}
+
+	ready, reason := r.CanAcceptTask(t.Context())
+	assert.False(t, ready)
+	assert.Contains(t, reason, "unhealthy")
+	assert.Equal(t, 1, calls)
+
+	fail = false
+	ready, _ = r.CanAcceptTask(t.Context())
+	assert.False(t, ready, "the failed result should remain cached")
+	assert.Equal(t, 1, calls)
+
+	now = now.Add(time.Minute)
+	ready, reason = r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+	assert.Equal(t, "ok", reason)
+	assert.Equal(t, 2, calls)
+}
+
+func TestConfiguredHealthCheckDisabled(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.HealthCheck.MinFreeDiskSpaceMB = 1 << 40
+	cfg.HealthCheck.Script = "/must-not-run"
+	r := &Runner{
+		cfg: cfg,
+		runHealthCheck: func(_ context.Context, _ string, _ time.Duration, _ map[string]string) error {
+			t.Fatal("disabled health check executed")
+			return nil
+		},
+	}
+	ready, reason := r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+	assert.Equal(t, "ok", reason)
+}
+
+func TestConfiguredHealthCheckDeferredWhileJobRuns(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.HealthCheck.Enabled = true
+	cfg.HealthCheck.Script = "/health-check"
+	cfg.HealthCheck.Interval = time.Minute
+
+	now := time.Now()
+	calls := 0
+	fail := false
+	r := &Runner{
+		cfg: cfg,
+		now: func() time.Time { return now },
+		runHealthCheck: func(_ context.Context, _ string, _ time.Duration, _ map[string]string) error {
+			calls++
+			if fail {
+				return errors.New("unhealthy")
+			}
+			return nil
+		},
+	}
+
+	ready, reason := r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+	assert.Equal(t, "ok", reason)
+	assert.Equal(t, 1, calls)
+
+	now = now.Add(time.Minute)
+	fail = true
+	r.runningCount.Store(1)
+	ready, reason = r.CanAcceptTask(t.Context())
+	assert.True(t, ready, "the last result should be reused while a job runs")
+	assert.Equal(t, "ok", reason)
+	assert.Equal(t, 1, calls)
+
+	r.runningCount.Store(0)
+	ready, reason = r.CanAcceptTask(t.Context())
+	assert.False(t, ready)
+	assert.Contains(t, reason, "unhealthy")
+	assert.Equal(t, 2, calls)
+}
+
+func TestConfiguredHealthCheckInitialRunDeferredWhileJobRuns(t *testing.T) {
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.HealthCheck.Enabled = true
+	cfg.HealthCheck.Script = "/health-check"
+
+	calls := 0
+	r := &Runner{
+		cfg: cfg,
+		runHealthCheck: func(_ context.Context, _ string, _ time.Duration, _ map[string]string) error {
+			calls++
+			return nil
+		},
+	}
+	r.runningCount.Store(1)
+
+	ready, reason := r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+	assert.Contains(t, reason, "deferred")
+	assert.Zero(t, calls)
+
+	r.runningCount.Store(0)
+	ready, reason = r.CanAcceptTask(t.Context())
+	assert.True(t, ready)
+	assert.Equal(t, "ok", reason)
+	assert.Equal(t, 1, calls)
+}

internal/app/run/runner.go

@@ -66,6 +66,13 @@ type Runner struct {
 	runningCount            atomic.Int64
 	lastIdleCleanupUnixNano atomic.Int64
 	now                     func() time.Time
+	healthCheckLast         time.Time
+	healthCheckReady        bool
+	healthCheckReason       string
+	healthStatusSet         bool
+	healthStatusReady       bool
+	healthStatusReason      string
+	runHealthCheck          func(context.Context, string, time.Duration, map[string]string) error
 }
 
 func NewRunner(cfg *config.Config, reg *config.Registration, cli client.Client) *Runner {
@@ -116,6 +123,7 @@ func NewRunner(cfg *config.Config, reg *config.Registration, cli client.Client)
 		envs:           envs,
 		cacheHandler:   cacheHandler,
 		now:            time.Now,
+		runHealthCheck: executeHealthCheck,
 	}
 	return runner
 }
@@ -579,6 +587,67 @@ func (r *Runner) RunningCount() int64 {
 	return r.runningCount.Load()
 }
 
+// CanAcceptTask checks local admission conditions without consuming a task. It is
+// called only from the poll loop, so the cached health fields need no lock.
+func (r *Runner) CanAcceptTask(ctx context.Context) (bool, string) {
+	if !r.cfg.HealthCheck.Enabled {
+		return true, "ok"
+	}
+
+	if r.RunningCount() > 0 {
+		if !r.healthStatusSet {
+			return true, "health checks deferred while jobs are running"
+		}
+		return r.healthStatusReady, r.healthStatusReason
+	}
+
+	if ready, reason := checkFreeDisk(r.cfg); !ready {
+		r.setHealthStatus(ready, reason)
+		return false, reason
+	}
+	ready, reason := r.checkConfiguredHealth(ctx)
+	r.setHealthStatus(ready, reason)
+	return ready, reason
+}
+
+func (r *Runner) setHealthStatus(ready bool, reason string) {
+	r.healthStatusSet = true
+	r.healthStatusReady = ready
+	r.healthStatusReason = reason
+}
+
+// checkFreeDisk evaluates the configured task-admission disk threshold.
+func checkFreeDisk(cfg *config.Config) (bool, string) {
+	root := cfg.Host.WorkdirParent
+	if cfg.Container.BindWorkdir {
+		root = filepath.FromSlash("/" + strings.TrimLeft(cfg.Container.WorkdirParent, "/"))
+	}
+	root = nearestExistingPath(root)
+	available, err := freeDiskBytes(root)
+	if err != nil {
+		return false, fmt.Sprintf("cannot determine free disk space for %s: %v", root, err)
+	}
+	availableMB := available / (1024 * 1024)
+	if availableMB < uint64(cfg.HealthCheck.MinFreeDiskSpaceMB) {
+		return false, fmt.Sprintf("low disk space on %s: %d MiB available, %d MiB required", root, availableMB, cfg.HealthCheck.MinFreeDiskSpaceMB)
+	}
+	return true, "ok"
+}
+
+func nearestExistingPath(path string) string {
+	for path != "" {
+		if _, err := os.Stat(path); err == nil {
+			return path
+		}
+		parent := filepath.Dir(path)
+		if parent == path {
+			return parent
+		}
+		path = parent
+	}
+	return "."
+}
+
 func (r *Runner) Declare(ctx context.Context, labels []string) (*connect.Response[runnerv1.DeclareResponse], error) {
 	return r.client.Declare(ctx, connect.NewRequest(&runnerv1.DeclareRequest{
 		Version:      ver.Version(),

internal/pkg/config/config.example.yaml

@@ -199,11 +199,29 @@ host:
   # If it's empty, $HOME/.cache/act/ will be used.
   workdir_parent:
 
+# Optional local task-admission checks. Disabled by default. When enabled, low
+# disk space or a failing script pauses new task fetching; existing jobs continue.
+# No health checks run while any job is active; the last result is reused until idle.
+health_check:
+  enabled: false
+  # Minimum free space required on the filesystem holding runner workspaces.
+  # Defaults to 1024 MiB when omitted or set to zero.
+  min_free_disk_space_mb: 1024
+  # Optional additional executable. A non-zero exit, timeout, or startup failure
+  # marks the runner unavailable.
+  script: ''
+  # How long a script result is cached and its maximum execution time.
+  interval: 30s
+  timeout: 10s
+
 metrics:
   # Enable the Prometheus metrics endpoint.
-  # When enabled, metrics are served at http://<addr>/metrics and a liveness check at /healthz.
+  # When enabled, metrics are served at /metrics, liveness at /healthz, and
+  # task-admission readiness at /readyz.
   enabled: false
   # The address for the metrics HTTP server to listen on.
   # Defaults to localhost only. Set to ":9101" to allow external access,
   # but ensure the port is firewall-protected as there is no authentication.
   addr: "127.0.0.1:9101"
+  # Consecutive polling failures may last this long before /readyz returns 503.
+  readiness_grace: 30s

internal/pkg/config/config.go

@@ -97,6 +97,17 @@ type Host struct {
 type Metrics struct {
 	Enabled        bool          `yaml:"enabled"`         // Enabled indicates whether the metrics endpoint is exposed.
 	Addr           string        `yaml:"addr"`            // Addr specifies the listen address for the metrics HTTP server (e.g., ":9101").
+	ReadinessGrace time.Duration `yaml:"readiness_grace"` // ReadinessGrace permits transient polling errors before /readyz becomes unhealthy.
+}
+
+// HealthCheck represents local checks that control whether the runner accepts
+// new tasks. The entire feature is opt-in through Enabled.
+type HealthCheck struct {
+	Enabled            bool          `yaml:"enabled"`                // Enabled activates local task-admission health checks.
+	MinFreeDiskSpaceMB int64         `yaml:"min_free_disk_space_mb"` // MinFreeDiskSpaceMB is the minimum free space required on the work volume.
+	Script             string        `yaml:"script"`                 // Script is an optional executable used as an additional health check.
+	Interval           time.Duration `yaml:"interval"`               // Interval controls how long a script result is cached.
+	Timeout            time.Duration `yaml:"timeout"`                // Timeout caps one health-check script invocation.
 }
 
 // Config represents the overall configuration.
@@ -107,6 +118,7 @@ type Config struct {
 	Container   Container   `yaml:"container"`    // Container represents the configuration for the container.
 	Host        Host        `yaml:"host"`         // Host represents the configuration for the host.
 	Metrics     Metrics     `yaml:"metrics"`      // Metrics represents the configuration for the Prometheus metrics endpoint.
+	HealthCheck HealthCheck `yaml:"health_check"` // HealthCheck controls opt-in local task-admission checks.
 }
 
 // LoadDefault returns the default configuration.
@@ -220,9 +232,21 @@ func LoadDefault(file string) (*Config, error) {
 	if cfg.Runner.PostTaskScript != "" && cfg.Runner.PostTaskScriptTimeout <= 0 {
 		cfg.Runner.PostTaskScriptTimeout = DefaultPostTaskScriptTimeout
 	}
+	if cfg.HealthCheck.MinFreeDiskSpaceMB <= 0 {
+		cfg.HealthCheck.MinFreeDiskSpaceMB = 1024
+	}
+	if cfg.HealthCheck.Interval <= 0 {
+		cfg.HealthCheck.Interval = 30 * time.Second
+	}
+	if cfg.HealthCheck.Timeout <= 0 {
+		cfg.HealthCheck.Timeout = 10 * time.Second
+	}
 	if cfg.Metrics.Addr == "" {
 		cfg.Metrics.Addr = "127.0.0.1:9101"
 	}
+	if cfg.Metrics.ReadinessGrace <= 0 {
+		cfg.Metrics.ReadinessGrace = 30 * time.Second
+	}
 
 	// Validate and fix invalid config combinations to prevent confusing behavior.
 	if cfg.Runner.FetchIntervalMax < cfg.Runner.FetchInterval {

internal/pkg/config/config_test.go

@@ -48,6 +48,41 @@ func TestLoadDefault_DefaultsWorkdirCleanupAge(t *testing.T) {
 	assert.Equal(t, 10*time.Minute, cfg.Runner.IdleCleanupInterval)
 }
 
+func TestLoadDefault_HealthChecksAreOptIn(t *testing.T) {
+	cfg, err := LoadDefault("")
+	require.NoError(t, err)
+	assert.False(t, cfg.HealthCheck.Enabled)
+	assert.Equal(t, int64(1024), cfg.HealthCheck.MinFreeDiskSpaceMB)
+	assert.Empty(t, cfg.HealthCheck.Script)
+	assert.Equal(t, 30*time.Second, cfg.HealthCheck.Interval)
+	assert.Equal(t, 10*time.Second, cfg.HealthCheck.Timeout)
+	assert.False(t, cfg.Metrics.Enabled)
+}
+
+func TestLoadDefault_DiskAndReadinessSettings(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte(`
+health_check:
+  enabled: true
+  min_free_disk_space_mb: 4096
+  script: /usr/local/bin/runner-health
+  interval: 15s
+  timeout: 3s
+metrics:
+  readiness_grace: 45s
+`), 0o600))
+
+	cfg, err := LoadDefault(path)
+	require.NoError(t, err)
+	assert.True(t, cfg.HealthCheck.Enabled)
+	assert.Equal(t, int64(4096), cfg.HealthCheck.MinFreeDiskSpaceMB)
+	assert.Equal(t, "/usr/local/bin/runner-health", cfg.HealthCheck.Script)
+	assert.Equal(t, 15*time.Second, cfg.HealthCheck.Interval)
+	assert.Equal(t, 3*time.Second, cfg.HealthCheck.Timeout)
+	assert.Equal(t, 45*time.Second, cfg.Metrics.ReadinessGrace)
+}
+
 func TestLoadDefault_UsesConfiguredWorkdirCleanupAge(t *testing.T) {
 	dir := t.TempDir()
 	path := filepath.Join(dir, "config.yaml")

internal/pkg/metrics/metrics_test.go

@@ -81,7 +81,7 @@ func TestRegisterRunningJobsFuncZeroCapacity(t *testing.T) {
 
 func TestStartServerCanBeCancelled(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
-	StartServer(ctx, "127.0.0.1:0")
+	StartServer(ctx, "127.0.0.1:0", nil)
 	cancel()
 }
 

internal/pkg/metrics/server.go

@@ -13,19 +13,12 @@ import (
 )
 
 // StartServer starts an HTTP server that serves Prometheus metrics on /metrics
-// and a liveness check on /healthz. The server shuts down when ctx is cancelled.
+// and health checks. The server shuts down when ctx is cancelled.
 // Call Init() before StartServer to register metrics with the Registry.
-func StartServer(ctx context.Context, addr string) {
+func StartServer(ctx context.Context, addr string, readiness func() (bool, string)) {
-	mux := http.NewServeMux()
-	mux.Handle("/metrics", promhttp.HandlerFor(Registry, promhttp.HandlerOpts{}))
-	mux.HandleFunc("/healthz", func(w http.ResponseWriter, _ *http.Request) {
-		w.WriteHeader(http.StatusOK)
-		_, _ = w.Write([]byte("ok"))
-	})
-
 	srv := &http.Server{
 		Addr:              addr,
-		Handler:           mux,
+		Handler:           NewHTTPHandler(readiness),
 		ReadHeaderTimeout: 5 * time.Second,
 		ReadTimeout:       10 * time.Second,
 		WriteTimeout:      10 * time.Second,
@@ -48,3 +41,25 @@ func StartServer(ctx context.Context, addr string) {
 		}
 	}()
 }
+
+// NewHTTPHandler returns the metrics and health endpoints used by StartServer.
+func NewHTTPHandler(readiness func() (bool, string)) http.Handler {
+	mux := http.NewServeMux()
+	mux.Handle("/metrics", promhttp.HandlerFor(Registry, promhttp.HandlerOpts{}))
+	mux.HandleFunc("/healthz", func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte("ok"))
+	})
+	mux.HandleFunc("/readyz", func(w http.ResponseWriter, _ *http.Request) {
+		ready, reason := true, "ok"
+		if readiness != nil {
+			ready, reason = readiness()
+		}
+		if !ready {
+			w.WriteHeader(http.StatusServiceUnavailable)
+		}
+		_, _ = w.Write([]byte(reason))
+	})
+
+	return mux
+}

internal/pkg/metrics/server_test.go

@@ -0,0 +1,43 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package metrics
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestReadyEndpoint(t *testing.T) {
+	tests := []struct {
+		name   string
+		ready  bool
+		reason string
+		status int
+	}{
+		{"ready", true, "ok", http.StatusOK},
+		{"not ready", false, "low disk space", http.StatusServiceUnavailable},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			handler := NewHTTPHandler(func() (bool, string) { return test.ready, test.reason })
+			request := httptest.NewRequest(http.MethodGet, "/readyz", nil)
+			response := httptest.NewRecorder()
+			handler.ServeHTTP(response, request)
+			assert.Equal(t, test.status, response.Code)
+			assert.Equal(t, test.reason, response.Body.String())
+		})
+	}
+}
+
+func TestHealthEndpointStaysLiveWhenNotReady(t *testing.T) {
+	handler := NewHTTPHandler(func() (bool, string) { return false, "low disk space" })
+	request := httptest.NewRequest(http.MethodGet, "/healthz", nil)
+	response := httptest.NewRecorder()
+	handler.ServeHTTP(response, request)
+	assert.Equal(t, http.StatusOK, response.Code)
+	assert.Equal(t, "ok", response.Body.String())
+}