metric-gate/proxy.go at master · sepich/metric-gate · GitHub

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package main

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/http"
	"net/url"
	"sync"
	"time"

	"github.com/prometheus/prometheus/model/labels"
	"github.com/prometheus/prometheus/model/relabel"
)

// Data model for aggregation
type Series struct {
	data map[string]*Seria // string = MetricName
	mu   sync.Mutex
}
type Seria map[string]*SVal // string = Labels.String()
type SVal struct {
	TimestampMs int64 // 0 = Now
	Value       float64
}

func NewSeries() *Series {
	return &Series{
		data: make(map[string]*Seria),
	}
}
func (s *Series) Add(metricName string, ls string, value SVal) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.data[metricName] == nil {
		tmp := make(Seria)
		tmp[ls] = &value
		s.data[metricName] = &tmp
	} else {
		tmp := *s.data[metricName]
		if tmp[ls] == nil {
			tmp[ls] = &value
		} else {
			tmp[ls].Value += value.Value
		}
	}
}

// Proxy handlers
type Proxy struct {
	Opts    Options
	logger  *slog.Logger
	subsets map[string]*Series
	tsMs    int64
}

func NewProxy(opts *Options, logger *slog.Logger) *Proxy {
	return &Proxy{Opts: *opts, logger: logger, subsets: make(map[string]*Series)}
}

// index returns help message
func (p *Proxy) index(w http.ResponseWriter, r *http.Request) {
	subsets := ""
	for s := range p.Opts.Relabel {
		if s != default_subset {
			subsets += fmt.Sprintf("\n<a href='/metrics/%s'>/metrics/%s</a> - aggregated and filtered metrics for subset '%s'<br/>", s, s, s)
		}
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(http.StatusOK)
	w.Write([]byte(`<html><body>
	<h1>metric-gate</h1>
	<a href='/source'>/source</a> - original metrics from upstream<br/>
	<a href='/analyze'>/analyze</a> - analyze upstream response for metrics and label cardinality<br/>
	<a href='/metrics'>/metrics</a> - aggregated and filtered metrics from upstream<br/>` + subsets + `
	<a href='/debug/pprof/'>/debug/pprof/</a> - pprof debug endpoints
	</body></html>`))
}

// src returns the response from upstream as is
func (p *Proxy) src(w http.ResponseWriter, r *http.Request) {
	resp, err := get(p.Opts.Upstream)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	defer resp.Body.Close()

	for name, values := range resp.Header {
		for _, value := range values {
			w.Header().Add(name, value)
		}
	}
	w.WriteHeader(resp.StatusCode)
	io.Copy(w, resp.Body)
}

// analyze returns metrics and label cardinality from upstream response
func (p *Proxy) analyze(w http.ResponseWriter, r *http.Request) {
	resp, err := get(p.Opts.Upstream)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	defer resp.Body.Close()

	data, err := parse(resp.Body)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	w.WriteHeader(http.StatusOK)
	w.Write([]byte(getReport(data)))
}

// agg returns aggregated filtered metrics
func (p *Proxy) agg(w http.ResponseWriter, r *http.Request) {
	start := time.Now()
	subset := r.PathValue("subset")
	if subset != "" {
		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
		if p.subsets[subset] == nil {
			w.WriteHeader(http.StatusBadRequest)
			w.Write([]byte("No metrics had been requested by /metrics yet or no such subset defined in relabel config"))
		} else {
			w.WriteHeader(http.StatusOK)
			render(p.subsets[subset], p.tsMs, w)
		}
		p.logger.Debug("Render subset metrics done", "took", time.Since(start))
		return
	}

	// reset subsets data
	subsets := make(map[string]*Series)
	for s := range p.Opts.Relabel {
		subsets[s] = NewSeries()
	}
	defer func() {
		for s := range p.Opts.Relabel {
			p.subsets[s] = subsets[s]
		}
	}()

	hosts := []string{p.Opts.Upstream}
	if p.Opts.Resolve != nil {
		ips, err := net.LookupIP(p.Opts.Resolve.Hostname())
		if err != nil {
			p.logger.Error("Error resolving upstream", "host", p.Opts.Resolve.Host, "err", err)
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		hosts = hosts[:0]
		for _, ip := range ips {
			hosts = append(hosts, ip.String())
		}
		p.logger.Debug("Resolved upstream", "hosts", hosts)
	}

	wg := sync.WaitGroup{}
	wg.Add(len(hosts))
	errCh := make(chan error, len(hosts))
	for _, h := range hosts {
		go func(host string) {
			defer wg.Done()
			p.scrape(host, subsets, errCh)
		}(h)
	}
	wg.Wait()
	close(errCh)
	p.logger.Debug("Upstream requests done", "took", time.Since(start), "upstreams", len(hosts), "down", len(errCh))

	if len(errCh) == len(hosts) {
		s := "Error getting any metrics from upstream:"
		for e := range errCh {
			s += "\n" + e.Error()
		}
		http.Error(w, s, http.StatusInternalServerError)
		return
	}
	p.tsMs = time.Now().UnixMilli()
	start = time.Now()
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	w.WriteHeader(http.StatusOK)
	render(subsets[default_subset], 0, w)
	p.logger.Debug("Render metrics done", "took", time.Since(start))
}

// scrape fetches metrics from `host` to subsets
func (p *Proxy) scrape(host string, subsets map[string]*Series, errCh chan error) {
	u := host
	if p.Opts.Resolve != nil {
		t := url.URL{
			Scheme:   p.Opts.Resolve.Scheme,
			Host:     host + ":" + p.Opts.Resolve.Port(),
			Path:     p.Opts.Resolve.Path,
			RawQuery: p.Opts.Resolve.RawQuery,
		}
		u = t.String()
	}
	ctx, cancel := context.WithTimeout(context.Background(), p.Opts.Timeout)
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, "GET", u, nil)
	if err != nil {
		p.logger.Error("Error creating request", "host", host, "err", err)
		errCh <- err
		return
	}
	if p.Opts.Resolve != nil {
		req.Host = p.Opts.Resolve.Hostname() // preserve the original Host header
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		p.logger.Error("Request failed", "host", host, "err", err)
		errCh <- err
		return
	}
	defer resp.Body.Close()

	err = p.parse(ctx, resp.Body, subsets)
	if err != nil {
		p.logger.Error("Error parsing response", "host", host, "err", err)
		errCh <- err
		return
	}
}

func get(url string) (*http.Response, error) {
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return nil, err
	}
	return http.DefaultClient.Do(req)
}

// parse unpacks and filters textformat
func (p *Proxy) parse(ctx context.Context, r io.Reader, series map[string]*Series) error {
	scanner := bufio.NewScanner(r)
	lb := labels.NewBuilder(labels.EmptyLabels())
	var n int
	for scanner.Scan() {
		line := scanner.Text()
		metricName, lbls, value, err := parseLine(line)
		if err != nil {
			if ctx.Err() != nil {
				p.logger.Warn("Scrape timeout reached, response truncated", "lines_parsed", n)
				return nil
			}
			return err
		}
		if metricName == "" {
			continue
		}

		// metric_relabel_configs
		for subset, mrc := range p.Opts.Relabel {
			lb.Reset(lbls)
			lb.Set("__name__", metricName)
			keep := relabel.ProcessBuilder(lb, mrc...)
			if !keep {
				continue
			}
			lb.Del("__name__")
			ls := labelsString(lb.Labels())
			series[subset].Add(metricName, ls, value)
		}
		n++
	}
	if err := scanner.Err(); err != nil && ctx.Err() != nil {
		p.logger.Warn("Scrape timeout reached, result truncated", "lines_parsed", n)
	}
	return nil
}

func render(series *Series, tsMs int64, w io.Writer) {
	for metricName, seria := range series.data {
		for labels, value := range *seria {
			w.Write([]byte(metricName))
			if len(labels) > 2 {
				w.Write([]byte(labels))
			}
			w.Write([]byte(fmt.Sprintf(" %#v", value.Value)))
			if value.TimestampMs > 0 {
				w.Write([]byte(fmt.Sprintf(" %d", value.TimestampMs)))
			} else if tsMs > 0 {
				w.Write([]byte(fmt.Sprintf(" %d", tsMs)))
			}
			w.Write([]byte("\n"))
		}
	}
}