Add enabled:false to disable a monitor while still listing it

Author: brvier

CHANGELOG.md

@@ -3,6 +3,14 @@
 All notable changes to Gjallar are documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## [0.8.0] - 2026-07-06
+
+### Added
+
+- `enabled: false` on a monitor: keep it on the status page (shown as a grey
+  DISABLED badge, excluded from the up/total count) without running any check
+  or alert. Defaults to enabled.
+
 ## [0.7.0] - 2026-07-06
 
 ### Added

README.md

@@ -62,6 +62,20 @@ Gjallar reloads its configuration on `SIGHUP` (`systemctl reload gjallar`).
 The new config is fully validated first — if it is broken, the running
 configuration is kept and the error is logged.
 
+### Disabling a monitor
+
+Set `enabled: false` on a monitor to stop checking and alerting on it while
+keeping it on the status page, shown with a grey **DISABLED** badge and
+excluded from the group's up/total count. Omitting `enabled` (or `true`)
+leaves it active.
+
+```yaml
+  - name: "legacy-api"
+    type: http
+    url: "http://legacy/health"
+    enabled: false      # listed as disabled, never checked
+```
+
 ### Groups
 
 Give monitors an optional `group: "Hyperion"` and the status page shows them

gjallar.example.yaml

@@ -43,6 +43,7 @@ monitors:
   # --- HTTP/HTTPS: status code, body regex, TLS certificate expiry ---
   - name: website
     group: "Public"    # optional: monitors sharing a group are shown together
+    # enabled: false   # optional: list it on the page as DISABLED, never check it
     type: http
     url: "https://example.com/api/health"
     method: GET                       # default GET

internal/alert/engine.go

@@ -43,6 +43,9 @@ type Engine struct {
 func NewEngine(cfg *config.Config, st *store.Store, notifiers map[string]Notifier) (*Engine, error) {
 	e := &Engine{st: st, notifiers: notifiers, states: map[string]*monitorState{}}
 	for _, m := range cfg.Monitors {
+		if !m.IsEnabled() {
+			continue // disabled monitors produce no results, need no state
+		}
 		s := &monitorState{threshold: m.FailureThreshold, realert: m.Realert.D(), notifiers: m.Alerts}
 		open, err := st.HasOpenIncident(m.Name)
 		if err != nil {

internal/config/config.go

@@ -60,8 +60,9 @@ type Alert struct {
 
 type Monitor struct {
 	Name             string   `yaml:"name"`
-	Group            string   `yaml:"group"` // optional; groups monitors on the status page
-	Type             string   `yaml:"type"`  // http | postgres | oracle | ping | prometheus
+	Group            string   `yaml:"group"`   // optional; groups monitors on the status page
+	Enabled          *bool    `yaml:"enabled"` // default true; false = listed but not checked
+	Type             string   `yaml:"type"`    // http | postgres | oracle | ping | prometheus
 	Interval         Duration `yaml:"interval"`
 	Timeout          Duration `yaml:"timeout"`
 	FailureThreshold int      `yaml:"failure_threshold"`
@@ -97,6 +98,11 @@ type Monitor struct {
 	TimestampField string `yaml:"timestamp_field"` // freshness = hours since max(this field)
 }
 
+// IsEnabled reports whether the monitor should be scheduled. A monitor with no
+// `enabled` key defaults to enabled; `enabled: false` lists it on the status
+// page as intentionally disabled without running any check or alert.
+func (m Monitor) IsEnabled() bool { return m.Enabled == nil || *m.Enabled }
+
 var monitorTypes = map[string]bool{
 	"http": true, "postgres": true, "oracle": true, "ping": true, "prometheus": true, "redis": true,
 	"elasticsearch": true,

internal/config/config_test.go

@@ -163,6 +163,35 @@ monitors:
 	}
 }
 
+func TestEnabledDefault(t *testing.T) {
+	cfg, err := Load(writeConfig(t, `
+monitors:
+  - name: a
+    type: ping
+    host: h
+  - name: b
+    type: ping
+    host: h
+    enabled: false
+  - name: c
+    type: ping
+    host: h
+    enabled: true
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !cfg.Monitors[0].IsEnabled() {
+		t.Error("a: default should be enabled")
+	}
+	if cfg.Monitors[1].IsEnabled() {
+		t.Error("b: enabled:false should be disabled")
+	}
+	if !cfg.Monitors[2].IsEnabled() {
+		t.Error("c: enabled:true should be enabled")
+	}
+}
+
 func TestLoadErrors(t *testing.T) {
 	cases := []struct {
 		name, yaml, wantErr string

internal/web/server.go

@@ -92,7 +92,8 @@ type IncidentView struct {
 type GroupView struct {
 	Name     string // empty = ungrouped
 	Up       int
-	Total    int
+	Total    int // enabled monitors only
+	Disabled int
 	Monitors []MonitorView
 }
 
@@ -164,6 +165,10 @@ func (s *Server) overview() overviewData {
 		}
 		g := &d.Groups[gi]
 		g.Monitors = append(g.Monitors, v)
+		if v.Status == "disabled" {
+			g.Disabled++
+			continue // disabled monitors don't count toward up/total health
+		}
 		g.Total++
 		if v.Status == "up" {
 			g.Up++
@@ -181,6 +186,10 @@ func (s *Server) overview() overviewData {
 
 func (s *Server) monitorView(m config.Monitor) MonitorView {
 	v := MonitorView{Name: m.Name, Type: m.Type, Status: "pending", Latency: "—", Uptime24h: "—"}
+	if !m.IsEnabled() {
+		v.Status = "disabled"
+		return v // no checks run, nothing to read from the store
+	}
 
 	results, err := s.st.RecentResults(m.Name, tickCount)
 	if err != nil {
@@ -229,12 +238,15 @@ func (s *Server) detail(name string) (detailData, bool) {
 		Type:   mon.Type,
 		Status: "pending", Uptime24h: "—", Uptime30d: "—",
 	}
+	if !mon.IsEnabled() {
+		d.Status = "disabled"
+	}
 	rows, err := s.st.RecentResults(name, historyCount)
 	if err != nil {
 		slog.Error("loading results", "monitor", name, "error", err)
 	}
 	d.Rows = rows
-	if len(rows) > 0 {
+	if mon.IsEnabled() && len(rows) > 0 {
 		if rows[0].OK {
 			d.Status = "up"
 		} else {

internal/web/static/style.css

@@ -82,6 +82,9 @@ h2 { border-left: 4px solid var(--red); padding-left: 10px; }
 .pill.up { background: #1f2a1f; color: var(--ok); border: 1px solid #3a4a3a; }
 .pill.down { background: var(--red-dark); color: #fff; border: 1px solid var(--red); }
 .pill.pending { background: #26262c; color: var(--muted); border: 1px solid var(--border); }
+.pill.disabled { background: #26262c; color: var(--muted); border: 1px dashed #4a4a52; }
+.card.disabled { opacity: .55; }
+.card.disabled .ticks { display: none; }
 
 /* uptime bars (oldest → newest) */
 .ticks { display: flex; gap: 2px; margin-top: 10px; }

internal/web/templates/_monitors.tmpl

@@ -3,12 +3,12 @@
 {{if .Name}}
 <div class="group-head">
   <h2>{{.Name}}</h2>
-  <span class="group-count{{if lt .Up .Total}} bad{{end}}">{{.Up}}/{{.Total}} up</span>
+  <span class="group-count{{if lt .Up .Total}} bad{{end}}">{{.Up}}/{{.Total}} up{{if .Disabled}} · {{.Disabled}} disabled{{end}}</span>
 </div>
 {{end}}
 <section class="cards">
 {{range .Monitors}}
-  <article class="card">
+  <article class="card{{if eq .Status "disabled"}} disabled{{end}}">
     <div class="card-head">
       <a class="mon-name" href="/monitor/{{.Name}}">{{.Name}}</a>
       <span class="mon-type">{{.Type}}</span>

main.go

@@ -113,6 +113,9 @@ func prepare(cfg *config.Config) (*prepared, error) {
 	p := &prepared{checkers: make([]check.Checker, len(cfg.Monitors))}
 	var err error
 	for i, m := range cfg.Monitors {
+		if !m.IsEnabled() {
+			continue // disabled monitors are listed but never built or run
+		}
 		if p.checkers[i], err = check.New(m); err != nil {
 			return nil, err
 		}
@@ -164,6 +167,9 @@ func start(cfg *config.Config, p *prepared) (*instance, error) {
 	// consumer (one SQLite writer, lock-free alert state machine).
 	results := make(chan check.Result, len(cfg.Monitors))
 	for i, m := range cfg.Monitors {
+		if !m.IsEnabled() {
+			continue // disabled: shown on the page, never scheduled
+		}
 		inst.runners.Add(1)
 		go func(m config.Monitor, c check.Checker) {
 			defer inst.runners.Done()
@@ -218,7 +224,7 @@ func (i *instance) stop() {
 func pingSelfTest(cfg *config.Config) error {
 	tested := map[bool]bool{}
 	for _, m := range cfg.Monitors {
-		if m.Type == "ping" && !tested[m.Privileged] {
+		if m.Type == "ping" && m.IsEnabled() && !tested[m.Privileged] {
 			tested[m.Privileged] = true
 			if err := check.SelfTestPing(m.Privileged); err != nil {
 				return err