fix: prometheus with multiple providers

we encountered an issue where tegola would panic if you'd try to register
duplicate metrics collectors.
that would happen if you have more than one mvt provider in the same config
file.

this fix makes provider metrics unique by adding the respective
provider name to an array of constant labels. Upon collecting metrics
on start up we'd pass unique metrics to the registration step.

resolves: #886

internal/build/build.go

@@ -8,7 +8,7 @@ import (
 )
 
 var (
-	Version              = "Version not set"
+	Version              = "version not set"
 	GitRevision          = "not set"
 	GitBranch            = "not set"
 	uiVersionDefaultText = "Viewer not build"

provider/postgis/postgis.go

@@ -34,6 +34,11 @@ const Name = "postgis"
 
 type connectionPoolCollector struct {
 	*pgxpool.Pool
+
+	// provider the pool is created for
+	// required to make metrics unique
+	providerName string
+
 	maxConnectionDesc        *prometheus.Desc
 	currentConnectionsDesc   *prometheus.Desc
 	availableConnectionsDesc *prometheus.Desc
@@ -47,7 +52,7 @@ func (c connectionPoolCollector) Collect(ch chan<- prometheus.Metric) {
 	if c.Pool == nil {
 		return
 	}
-	stat := c.Pool.Stat()
+	stat := c.Stat()
 	ch <- prometheus.MustNewConstMetric(
 		c.maxConnectionDesc,
 		prometheus.GaugeValue,
@@ -73,33 +78,38 @@ func (c *connectionPoolCollector) Collectors(prefix string, _ func(configKey str
 		prefix = prefix + "_"
 	}
 
+	// a constant label ensures that the metrics are unique
+	// this allows the registration of multiple providers in the same
+	// config.
 	c.maxConnectionDesc = prometheus.NewDesc(
 		prefix+"postgres_max_connections",
 		"Max number of postgres connections in the pool",
 		nil,
-		nil,
+		prometheus.Labels{"provider_name": c.providerName},
 	)
 
 	c.currentConnectionsDesc = prometheus.NewDesc(
 		prefix+"postgres_current_connections",
 		"Current number of postgres connections in the pool",
 		nil,
-		nil,
+		prometheus.Labels{"provider_name": c.providerName},
 	)
 
 	c.availableConnectionsDesc = prometheus.NewDesc(
 		prefix+"postgres_available_connections",
 		"Current number of available postgres connections in the pool",
 		nil,
-		nil,
+		prometheus.Labels{"provider_name": c.providerName},
 	)
 	return []observability.Collector{c}, nil
 }
 
 // Provider provides the postgis data provider.
 type Provider struct {
 	config pgxpool.Config
+	name   string
 	pool   *connectionPoolCollector
+
 	// map of layer name and corresponding sql
 	layers     map[string]Layer
 	srid       uint64
@@ -122,31 +132,37 @@ func (p *Provider) Collectors(prefix string, cfgFn func(configKey string) map[st
 	}
 
 	buckets := []float64{.1, 1, 5, 20}
-	collectors, err := p.pool.Collectors(prefix, cfgFn)
+	c, err := p.pool.Collectors(prefix, cfgFn)
 	if err != nil {
 		return nil, err
 	}
 
+	// a constant label ensures that the metrics are unique
+	// this allows the registration of multiple providers in the same
+	// config.
+	// Additional label names will be appended to the constant labels.
 	p.mvtProviderQueryHistogramSeconds = prometheus.NewHistogramVec(
 		prometheus.HistogramOpts{
-			Name:    prefix + "_mvt_provider_sql_query_seconds",
-			Help:    "A histogram of query time for sql for mvt providers",
-			Buckets: buckets,
+			Name:        prefix + "_mvt_provider_sql_query_seconds",
+			Help:        "A histogram of query time for sql for mvt providers",
+			Buckets:     buckets,
+			ConstLabels: prometheus.Labels{"provider_name": p.name},
 		},
 		[]string{"map_name", "z"},
 	)
 
 	p.queryHistogramSeconds = prometheus.NewHistogramVec(
 		prometheus.HistogramOpts{
-			Name:    prefix + "_provider_sql_query_seconds",
-			Help:    "A histogram of query time for sql for providers",
-			Buckets: buckets,
+			Name:        prefix + "_provider_sql_query_seconds",
+			Help:        "A histogram of query time for sql for providers",
+			Buckets:     buckets,
+			ConstLabels: prometheus.Labels{"provider_name": p.name},
 		},
 		[]string{"map_name", "layer_name", "z"},
 	)
 
 	p.collectorsRegistered = true
-	return append(collectors, p.mvtProviderQueryHistogramSeconds, p.queryHistogramSeconds), nil
+	return append(c, p.mvtProviderQueryHistogramSeconds, p.queryHistogramSeconds), nil
 }
 
 const (
@@ -460,20 +476,26 @@ func CreateProvider(config dict.Dicter, maps []provider.Map, providerType string
 		return nil, err
 	}
 
+	name, err := config.String(ConfigKeyName, nil)
+	if err != nil {
+		return nil, err
+	}
+
 	if err = ConfigTLS(sslmode, sslkey, sslcert, sslrootcert, dbconfig); err != nil {
 		return nil, err
 	}
 
 	p := Provider{
 		srid:   uint64(srid),
 		config: *dbconfig,
+		name:   name,
 	}
 
 	pool, err := pgxpool.ConnectConfig(context.Background(), &p.config)
 	if err != nil {
 		return nil, fmt.Errorf("failed while creating connection pool: %w", err)
 	}
-	p.pool = &connectionPoolCollector{Pool: pool}
+	p.pool = &connectionPoolCollector{Pool: pool, providerName: name}
 
 	layers, err := config.MapSlice(ConfigKeyLayers)
 	if err != nil {

server/server.go

@@ -3,11 +3,12 @@ package server
 
 import (
 	"fmt"
-	"github.com/go-spatial/tegola/internal/build"
 	"net/http"
 	"net/url"
 	"path"
 
+	"github.com/go-spatial/tegola/internal/build"
+
 	"github.com/go-spatial/tegola/observability"
 
 	"github.com/dimfeld/httptreemux"
@@ -25,7 +26,7 @@ const (
 var (
 	// Version is the version of the software, this should be set by the main program, before starting up.
 	// It is used by various Middleware to determine the version.
-	Version string = "Version Not Set"
+	Version string = "version not set"
 
 	// HostName is the name of the host to use for construction of URLS.
 	// configurable via the tegola config.toml file (set in main.go)
@@ -71,7 +72,7 @@ func NewRouter(a *atlas.Atlas) *httptreemux.TreeMux {
 		)
 		if h := o.Handler(metricsRoute); h != nil {
 			// Only set up the /metrics endpoint if we have a configured observer
-			log.Infof("Setting up observer: %v", o.Name())
+			log.Infof("setting up observer: %v", o.Name())
 			group.UsingContext().Handler(http.MethodGet, metricsRoute, h)
 		}
 	}
@@ -98,7 +99,7 @@ func NewRouter(a *atlas.Atlas) *httptreemux.TreeMux {
 func Start(a *atlas.Atlas, port string) *http.Server {
 
 	// notify the user the server is starting
-	log.Infof("starting tegola server(%v) on port %v", build.Version, port)
+	log.Infof("starting tegola server (%v) on port %v", build.Version, port)
 
 	srv := &http.Server{Addr: port, Handler: NewRouter(a)}