e2e: Generate prometheus.yaml on setup (#954) (#957)

* Generate prometheus yaml on setup

* change file extension

* move template to file

* add templates dir

(cherry picked from commit 3701c9f3c1a12a0ce35cef98788bdebb382bd74e)

Co-authored-by: Hernán Vanzetto <[email protected]>

test/e2e/pkg/templates/prometheus-yaml.tmpl

@@ -0,0 +1,9 @@
+global:
+  scrape_interval: 1s
+
+scrape_configs:
+{{- range .Nodes }}
+  - job_name: '{{ .Name }}'
+    static_configs:
+      - targets: ['localhost:{{ .PrometheusProxyPort }}']
+{{end}}

test/e2e/pkg/testnet.go

@@ -1,21 +1,26 @@
 package e2e
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"math/rand"
 	"net"
+	"os"
 	"path/filepath"
 	"sort"
 	"strconv"
 	"strings"
+	"text/template"
 	"time"
 
 	"github.com/cometbft/cometbft/crypto"
 	"github.com/cometbft/cometbft/crypto/ed25519"
 	"github.com/cometbft/cometbft/crypto/secp256k1"
 	rpchttp "github.com/cometbft/cometbft/rpc/client/http"
+
+	_ "embed"
 )
 
 const (
@@ -470,6 +475,34 @@ func (t Testnet) HasPerturbations() bool {
 	return false
 }
 
+//go:embed templates/prometheus-yaml.tmpl
+var prometheusYamlTemplate string
+
+func (t Testnet) prometheusConfigBytes() ([]byte, error) {
+	tmpl, err := template.New("prometheus-yaml").Parse(prometheusYamlTemplate)
+	if err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	err = tmpl.Execute(&buf, t)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func (t Testnet) WritePrometheusConfig() error {
+	bytes, err := t.prometheusConfigBytes()
+	if err != nil {
+		return err
+	}
+	err = os.WriteFile(filepath.Join(t.Dir, "prometheus.yaml"), bytes, 0o644) //nolint:gosec
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 // Address returns a P2P endpoint address for the node.
 func (n Node) AddressP2P(withID bool) string {
 	ip := n.IP.String()

test/e2e/runner/setup.go

@@ -116,6 +116,12 @@ func Setup(testnet *e2e.Testnet, infp infra.Provider) error {
 		)).Save()
 	}
 
+	if testnet.Prometheus {
+		if err := testnet.WritePrometheusConfig(); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }