Backend Services

Each extension backend is a Go HTTP server that queries the underlying system and exposes a JSON API consumed by the UI via ArgoCD’s proxy.

HTTP handlers

Use Go 1.22+ routing patterns:

mux := http.NewServeMux()
mux.HandleFunc("GET /api/v1/metrics", s.handleMetrics)
mux.HandleFunc("GET /api/v1/backups", s.handleBackups)
mux.HandleFunc("POST /api/v1/backups/{name}/restore", s.handleRestore)

ArgoCD identity headers

Backend services receive identity headers from ArgoCD’s proxy. Use them for authorization and scoping:

func userFromRequest(r *http.Request) (username, userID string, groups []string) {
    username = r.Header.Get("Argocd-Username")
    userID = r.Header.Get("Argocd-User-Id")
    groups = strings.Split(r.Header.Get("Argocd-User-Groups"), ",")
    return
}

func clusterFromRequest(r *http.Request) (name, url string) {
    name = r.Header.Get("Argocd-Target-Cluster-Name")
    url = r.Header.Get("Argocd-Target-Cluster-URL")
    return
}

Configuration

Use envconfig struct tags. Load in main(), pass values to constructors:

type Config struct {
    Port          string `envconfig:"PORT" default:"8080"`
    PrometheusURL string `envconfig:"PROMETHEUS_URL" required:"true"`
    LogLevel      string `envconfig:"LOG_LEVEL" default:"info"`
}

Error handling

Always wrap errors with context:

if err != nil {
    return nil, fmt.Errorf("failed to fetch backups: %w", err)
}

Logging

Use log/slog with structured key-value pairs:

slog.Info("querying prometheus", "url", config.PrometheusURL, "query", query)
slog.Error("failed to fetch backups", "error", err, "namespace", ns)

Import organization

Three groups separated by blank lines: stdlib, external, internal:

import (
    "context"
    "fmt"
    "net/http"

    "github.com/prometheus/client_golang/api"

    "github.com/natrontech/argoplane/extensions/metrics/internal/query"
)

Graceful shutdown

ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
defer stop()

srv := &http.Server{Addr: ":" + config.Port, Handler: mux}

go func() {
    <-ctx.Done()
    srv.Shutdown(context.Background())
}()

srv.ListenAndServe()

Naming conventions

Constructors: New<Type>(...) (*Type, error)
Method receivers: short names (s *Server, c *Client)
No Get/List prefixes: Backups() not GetBackups()
Packages: single lowercase word (metrics, backups, proxy)