Add configuration options and enable dynamic memory management through cc-backend callback

internal/api/nodeprovider.go

@@ -0,0 +1,54 @@
+// Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
+// All rights reserved. This file is part of cc-metric-store.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package api
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// BackendNodeProvider implements metricstore.NodeProvider by querying
+// the cc-backend /api/jobs/used_nodes endpoint.
+type BackendNodeProvider struct {
+	backendUrl string
+	client     *http.Client
+}
+
+// NewBackendNodeProvider creates a new BackendNodeProvider that queries
+// the given cc-backend URL for used nodes information.
+func NewBackendNodeProvider(backendUrl string) *BackendNodeProvider {
+	return &BackendNodeProvider{
+		backendUrl: backendUrl,
+		client: &http.Client{
+			Timeout: 10 * time.Second,
+		},
+	}
+}
+
+// GetUsedNodes returns a map of cluster names to sorted lists of unique hostnames
+// that are currently in use by jobs that started before the given timestamp.
+func (p *BackendNodeProvider) GetUsedNodes(ts int64) (map[string][]string, error) {
+	url := fmt.Sprintf("%s/api/jobs/used_nodes?ts=%d", p.backendUrl, ts)
+
+	resp, err := p.client.Get(url)
+	if err != nil {
+		return nil, fmt.Errorf("querying used nodes from backend: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("backend returned status %d", resp.StatusCode)
+	}
+
+	var result map[string][]string
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return nil, fmt.Errorf("decoding used nodes response: %w", err)
+	}
+
+	return result, nil
+}