[feature] Add healthcheck endpoints /livez and /readyz (#2783)

* [feature] Add healthcheck endpoints `/livez` and `/readyz`

* use select that returns no data

internal/api/health.go

@@ -0,0 +1,51 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package api
+
+import (
+	"context"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/api/health"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
+	"github.com/superseriousbusiness/gotosocial/internal/router"
+)
+
+type Health struct {
+	health *health.Module
+}
+
+func (mt *Health) Route(r *router.Router, m ...gin.HandlerFunc) {
+	// Create new group on top level prefix.
+	healthGroup := r.AttachGroup("")
+	healthGroup.Use(m...)
+	healthGroup.Use(
+		middleware.CacheControl(middleware.CacheControlConfig{
+			// Never cache health responses.
+			Directives: []string{"no-store"},
+		}),
+	)
+
+	mt.health.Route(healthGroup.Handle)
+}
+
+func NewHealth(readyF func(context.Context) error) *Health {
+	return &Health{
+		health: health.New(readyF),
+	}
+}

internal/api/health/health.go

@@ -0,0 +1,48 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package health
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+const (
+	LivePath  = "/livez"
+	ReadyPath = "/readyz"
+)
+
+type Module struct {
+	readyF func(context.Context) error
+}
+
+func New(readyF func(context.Context) error) *Module {
+	return &Module{
+		readyF: readyF,
+	}
+}
+
+func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
+	attachHandler(http.MethodGet, LivePath, m.LiveGETRequest)
+	attachHandler(http.MethodHead, LivePath, m.LiveHEADRequest)
+
+	attachHandler(http.MethodGet, ReadyPath, m.ReadyGETRequest)
+	attachHandler(http.MethodHead, ReadyPath, m.ReadyHEADRequest)
+}

internal/api/health/live.go

@@ -0,0 +1,54 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package health
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// LiveGETRequest swagger:operation GET /livez liveGet
+//
+// Returns code 200 with no body if GoToSocial is "live", ie., able to respond to HTTP requests.
+//
+//	---
+//	tags:
+//	- health
+//
+//	responses:
+//		'200':
+//			description: OK
+func (m *Module) LiveGETRequest(c *gin.Context) {
+	c.Status(http.StatusOK)
+}
+
+// LiveHEADRequest swagger:operation HEAD /livez liveHead
+//
+// Returns code 200 if GoToSocial is "live", ie., able to respond to HTTP requests.
+//
+//	---
+//	tags:
+//	- health
+//
+//	responses:
+//		'200':
+//			description: OK
+func (m *Module) LiveHEADRequest(c *gin.Context) {
+	c.Status(http.StatusOK)
+}

internal/api/health/ready.go

@@ -0,0 +1,74 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package health
+
+import (
+	"net/http"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+
+	"github.com/gin-gonic/gin"
+)
+
+func (m *Module) ready(c *gin.Context) {
+	if err := m.readyF(c.Request.Context()); err != nil {
+		// Set error on the gin context so
+		// it's logged by the logging middleware.
+		errWithCode := gtserror.NewErrorInternalError(err)
+		c.Error(errWithCode) //nolint:errcheck
+		c.Status(http.StatusInternalServerError)
+	} else {
+		c.Status(http.StatusOK)
+	}
+}
+
+// ReadyGETRequest swagger:operation GET /readyz readyGet
+//
+// Returns code 200 with no body if GoToSocial is "ready", ie., able to connect to the database backend and do a simple SELECT.
+//
+// If GtS is not ready, 500 Internal Error will be returned, and an error will be logged (but not returned to the caller, to avoid leaking internals).
+//
+//	---
+//	tags:
+//	- health
+//
+//	responses:
+//		'200':
+//			description: OK
+//		'500':
+//			description: Not ready. Check logs for error message.
+func (m *Module) ReadyGETRequest(c *gin.Context) {
+	m.ready(c)
+}
+
+// ReadyHEADRequest swagger:operation HEAD /readyz readyHead
+//
+// Returns code 200 with no body if GoToSocial is "ready", ie., able to connect to the database backend and do a simple SELECT.
+//
+// If GtS is not ready, 500 Internal Error will be returned, and an error will be logged (but not returned to the caller, to avoid leaking internals).
+//
+//	---
+//	tags:
+//	- health
+//
+//	responses:
+//		'200':
+//			description: OK
+func (m *Module) ReadyHEADRequest(c *gin.Context) {
+	m.ready(c)
+}

internal/db/basic.go

@@ -33,8 +33,8 @@ type Basic interface {
 	// If the database implementation doesn't need to be stopped, this can just return nil.
 	Close() error
 
-	// IsHealthy should return nil if the database connection is healthy, or an error if not.
-	IsHealthy(ctx context.Context) error
+	// Ready returns nil if the database connection is ready, or an error if not.
+	Ready(ctx context.Context) error
 
 	// GetByID gets one entry by its id. In a database like postgres, this might be the 'id' field of the entry,
 	// for other implementations (for example, in-memory) it might just be the key of a map.

internal/db/bundb/basic.go

@@ -124,8 +124,14 @@ func (b *basicDB) DropTable(ctx context.Context, i interface{}) error {
 	return err
 }
 
-func (b *basicDB) IsHealthy(ctx context.Context) error {
-	return b.db.PingContext(ctx)
+func (b *basicDB) Ready(ctx context.Context) error {
+	if _, err := b.db.
+		NewRaw("SELECT NULL FROM ? LIMIT 0", bun.Ident("instances")).
+		Exec(ctx); err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func (b *basicDB) Close() error {