Add metrics endpoints

backend/api/spec.yaml

@@ -1177,6 +1177,53 @@ paths:
           description: Activity not found response
         "500":
           description: List activity error response
+  /instance-metrics/prometheus:
+    get:
+      description: Get latest instance stats
+      operationId: getLatestInstanceStats
+      security:
+        - oidcBearerAuth: []
+        - oidcCookieAuth: []
+        - githubCookieAuth: []
+      responses:
+        "200":
+          description: Get latest instance stats success response
+          content:
+            text/plain:
+              schema:
+                type: string
+        "500":
+          description: Get latest instance stats error response
+  /instance-metrics/json:
+    get:
+      description: Get instance stats
+      operationId: getInstanceStats
+      parameters:
+        - in: query
+          name: page
+          required: false
+          schema:
+            type: integer
+            minimum: 0
+        - in: query
+          name: perpage
+          required: false
+          schema:
+            type: integer
+            minimum: 10
+      security:
+        - oidcBearerAuth: []
+        - oidcCookieAuth: []
+        - githubCookieAuth: []
+      responses:
+        "200":
+          description: List instance stats response
+          content:
+            application/x-ndjson:
+              schema:
+                $ref: "#/components/schemas/instanceStats"
+        "500":
+          description: Get instance stats error response
 components:
   schemas:
     ## request Body
@@ -1339,6 +1386,46 @@ components:
         package_id:
           type: string
 
+    instanceStatsPage:
+      type: object
+      required:
+        - totalCount
+        - count
+        - applications
+      properties:
+        totalCount:
+          type: integer
+        count:
+          type: integer
+        applications:
+          type: array
+          items:
+            $ref: "#/components/schemas/instanceStats"
+
+    instanceStats:
+      type: object
+      required:
+        - type
+        - channel
+        - version
+        - arch
+        - timestamp
+        - instances
+      properties:
+        type:
+          type: string
+          enum: ["instance_count"]
+        channel:
+          type: string
+        version:
+          type: string
+        arch:
+          type: string
+        timestamp:
+          type: string
+        count:
+          type: integer
+
 
     ## response     
     config:

backend/pkg/api/instances.go

@@ -723,11 +723,24 @@ func (api *API) instanceStatsQuery(t *time.Time, duration *time.Duration) *goqu.
 	return query
 }
 
+// GetInstanceStatsCount returns the total number of InstanceStats.
+func (api *API) GetInstanceStatsCount() (int, error) {
+	query := goqu.From("instance_stats").Select(goqu.L("count(*)"))
+	return api.GetCountQuery(query)
+}
+
 // GetInstanceStats returns an InstanceStats table with all instances that have
 // been previously been checked in.
-func (api *API) GetInstanceStats() ([]InstanceStats, error) {
-	query, _, err := goqu.From("instance_stats").
-		Order(goqu.C("timestamp").Asc()).ToSQL()
+func (api *API) GetInstanceStats(page, perPage uint64) ([]InstanceStats, error) {
+	page, perPage = validatePaginationParams(page, perPage)
+	limit, offset := sqlPaginate(page, perPage)
+
+	query, _, err := goqu.
+		From("instance_stats").
+		Limit(limit).
+		Offset(offset).
+		Order(goqu.C("timestamp").Asc()).
+		ToSQL()
 	if err != nil {
 		return nil, err
 	}

backend/pkg/api/instances_test.go

@@ -300,7 +300,7 @@ func TestUpdateInstanceStats(t *testing.T) {
 	a := newForTest(t)
 	defer a.Close()
 
-	instances, err := a.GetInstanceStats()
+	instances, err := a.GetInstanceStats(1, 100)
 	assert.NoError(t, err)
 	assert.Equal(t, 0, len(instances))
 
@@ -328,7 +328,7 @@ func TestUpdateInstanceStats(t *testing.T) {
 	err = a.UpdateInstanceStats(&ts, &elapsed)
 	assert.NoError(t, err)
 
-	instances, err = a.GetInstanceStats()
+	instances, err = a.GetInstanceStats(1, 100)
 	assert.NoError(t, err)
 	assert.Equal(t, 2, len(instances))
 
@@ -357,7 +357,7 @@ func TestUpdateInstanceStats(t *testing.T) {
 	err = a.UpdateInstanceStats(&ts3, &elapsed)
 	assert.NoError(t, err)
 
-	instances, err = a.GetInstanceStats()
+	instances, err = a.GetInstanceStats(1, 100)
 	assert.NoError(t, err)
 	assert.Equal(t, 5, len(instances))
 

backend/pkg/api/metrics.go

@@ -21,6 +21,12 @@ WHERE a.id = e.application_id AND e.event_type_id = et.id AND et.result = 0 AND
 GROUP BY app_name
 ORDER BY app_name
 `, ignoreFakeInstanceCondition("e.instance_id"))
+
+	latestInstanceStatsSQL = `
+SELECT channel_name, version, arch, timestamp, instances AS instances_count
+FROM instance_stats
+WHERE timestamp = (SELECT MAX(timestamp) FROM instance_stats)
+`
 )
 
 type AppInstancesPerChannelMetric struct {
@@ -77,6 +83,38 @@ func (api *API) GetFailedUpdatesMetrics() ([]FailedUpdatesMetric, error) {
 	return metrics, nil
 }
 
+type LatestInstanceStatsMetric struct {
+	ChannelName    string `db:"channel_name" json:"channel_name"`
+	Version        string `db:"version" json:"version"`
+	Arch           string `db:"arch" json:"arch"`
+	Timestamp      string `db:"timestamp" json:"timestamp"`
+	InstancesCount int    `db:"instances_count" json:"instances_count"`
+}
+
+func (api *API) GetLatestInstanceStatsMetrics() ([]LatestInstanceStatsMetric, error) {
+	var metrics []LatestInstanceStatsMetric
+	rows, err := api.db.Queryx(latestInstanceStatsSQL)
+	if err != nil {
+		return nil, fmt.Errorf("querying latest instance stats from SQL: %w", err)
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var metric LatestInstanceStatsMetric
+		if err := rows.StructScan(&metric); err != nil {
+			return nil, fmt.Errorf("scanning instance stat metric: %w", err)
+		}
+
+		metrics = append(metrics, metric)
+	}
+
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+
+	return metrics, nil
+}
+
 func (api *API) DbStats() sql.DBStats {
 	return api.db.Stats()
 }