kg: add new handler for rendering the topology graph via the metrics webserver

Dockerfile

@@ -11,7 +11,7 @@ ARG GOARCH
 ARG ALPINE_VERSION=v3.12
 LABEL maintainer="squat <lserven@gmail.com>"
 RUN echo -e "https://alpine.global.ssl.fastly.net/alpine/$ALPINE_VERSION/main\nhttps://alpine.global.ssl.fastly.net/alpine/$ALPINE_VERSION/community" > /etc/apk/repositories && \
-    apk add --no-cache ipset iptables ip6tables wireguard-tools
+    apk add --no-cache ipset iptables ip6tables wireguard-tools graphviz font-bitstream-type1
 COPY --from=cni bridge host-local loopback portmap /opt/cni/bin/
 COPY bin/linux/$GOARCH/kg /opt/bin/
 ENTRYPOINT ["/opt/bin/kg"]

cmd/kg/handlers.go

@@ -0,0 +1,132 @@
+// Copyright 2019 the Kilo authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"mime"
+	"net/http"
+	"os"
+	"os/exec"
+
+	"github.com/squat/kilo/pkg/mesh"
+)
+
+type GraphHandler struct {
+	mesh        *mesh.Mesh
+	granularity mesh.Granularity
+}
+
+func (h *GraphHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	ns, err := h.mesh.Nodes().List()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to list nodes: %v", err), 500)
+		return
+	}
+	ps, err := h.mesh.Peers().List()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to list peers: %v", err), 500)
+		return
+	}
+
+	var hostname string
+	subnet := mesh.DefaultKiloSubnet
+	nodes := make(map[string]*mesh.Node)
+	for _, n := range ns {
+		if n.Ready() {
+			nodes[n.Name] = n
+			hostname = n.Name
+		}
+		if n.WireGuardIP != nil {
+			subnet = n.WireGuardIP
+		}
+	}
+	subnet.IP = subnet.IP.Mask(subnet.Mask)
+	if len(nodes) == 0 {
+		http.Error(w, "did not find any valid Kilo nodes in the cluster", 500)
+		return
+	}
+	peers := make(map[string]*mesh.Peer)
+	for _, p := range ps {
+		if p.Ready() {
+			peers[p.Name] = p
+		}
+	}
+	topo, err := mesh.NewTopology(nodes, peers, h.granularity, hostname, 0, []byte{}, subnet, nodes[hostname].PersistentKeepalive, nil)
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to create topology: %v", err), 500)
+		return
+	}
+
+	dot, err := topo.Dot()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("failed to generate graph: %v", err), 500)
+	}
+
+	buf := bytes.NewBufferString(dot)
+
+	format := r.URL.Query().Get("format")
+	if format == "" {
+		format = "png"
+	} else if format == ".dot" || format == ".gv" {
+		// If the raw dot data is requested, return it as string.
+		// This allows client-side rendering rather than server-side.
+		w.Write(buf.Bytes())
+		return
+	}
+
+	command := exec.Command("dot", "-T"+format)
+	command.Stderr = os.Stderr
+
+	stdin, err := command.StdinPipe()
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	_, err = io.Copy(stdin, buf)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	err = stdin.Close()
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	output, err := command.Output()
+	if err != nil {
+		http.Error(w, fmt.Sprintf("unable to execute dot: %v (is graphviz package installed?)", err), 500)
+		return
+	}
+
+	mimeType := mime.TypeByExtension("." + format)
+	if mimeType == "" {
+		mimeType = "application/octet-stream"
+	}
+
+	w.Write(output)
+}
+
+type HealthHandler struct {
+}
+
+func (h *HealthHandler) ServeHTTP(w http.ResponseWriter, _ *http.Request) {
+	w.WriteHeader(http.StatusOK)
+}

cmd/kg/main.go

@@ -196,9 +196,8 @@ func Main() error {
 	{
 		// Run the HTTP server.
 		mux := http.NewServeMux()
-		mux.HandleFunc("/health", func(w http.ResponseWriter, _ *http.Request) {
-			w.WriteHeader(http.StatusOK)
-		})
+		mux.Handle("/health", &HealthHandler{})
+		mux.Handle("/graph", &GraphHandler{m, gr})
 		mux.Handle("/metrics", promhttp.HandlerFor(r, promhttp.HandlerOpts{}))
 		l, err := net.Listen("tcp", *listen)
 		if err != nil {