Provide contract address via http (#2303)

* Add contract-address webserver

* add comment

* printf

k8s/beacon-chain/contract-address.yaml

@@ -0,0 +1,74 @@
+kind: Deployment
+apiVersion: apps/v1
+metadata: 
+  name: contract-address-http
+  namespace: beacon-chain
+  labels:
+    app: beacon-chain
+    component: contract-address-http
+    version: v1
+spec:
+  replicas: 2
+  selector:
+    matchLabels:
+      app: beacon-chain
+      component: contract-address-http
+      version: v1
+  template:
+    metadata:
+      labels:
+        app: beacon-chain
+        component: contract-address-http
+        version: v1
+    spec:
+      priorityClassName: production-priority
+      containers:
+      - name: site
+        image: gcr.io/prysmaticlabs/prysm/contract-addr:latest
+        args:
+          - --address-path=/etc/address/DEPOSIT_CONTRACT_ADDRESS
+        ports: 
+        - containerPort: 8080
+          name: http
+        volumeMounts:
+        - name: config-volume
+          mountPath: /etc/address
+      volumes:
+      - name: config-volume
+        configMap:
+          name: beacon-config
+---
+kind: Service
+apiVersion: v1
+metadata: 
+  name: contract-address-http
+  namespace: beacon-chain
+spec:
+  selector:
+    app: beacon-chain
+    component: contract-address-http
+  ports:
+  - port: 8080
+    targetPort: 8080
+    name: http
+  type: ClusterIP
+---
+apiVersion: networking.istio.io/v1alpha3
+kind: VirtualService
+metadata: 
+  name: contract-address-http
+  namespace: istio-system
+spec:
+  hosts:
+  - beta.prylabs.net
+  gateways:
+  - prylabs-wildcard-gateway
+  http:
+  - match:
+    - uri:
+        prefix: /contract
+    route:
+    - destination:
+        port:
+          number: 8080
+        host: contract-address-http.beacon-chain.svc.cluster.local

tools/contract-addr/BUILD.bazel

@@ -0,0 +1,42 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("@io_bazel_rules_docker//go:image.bzl", "go_image")
+load("@io_bazel_rules_docker//container:container.bzl", "container_push")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["main.go"],
+    importpath = "github.com/prysmaticlabs/prysm/tools/contract-addr",
+    visibility = ["//visibility:private"],
+)
+
+go_binary(
+    name = "contract-addr",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)
+
+go_image(
+    name = "image",
+    srcs = ["main.go"],
+    importpath = "github.com/prysmaticlabs/prysm/tools/contract-addr",
+    visibility = ["//visibility:private"],
+    static = "on",
+    tags = ["manual"],
+    goarch = "amd64",
+    goos = "linux",
+    deps = [
+    ],
+    race = "off",
+    pure = "on",
+)
+
+container_push(
+    name = "push_image",
+    format = "Docker",
+    image = ":image",
+    registry = "gcr.io",
+    repository = "prysmaticlabs/prysm/contract-addr",
+    tag = "latest",
+    tags = ["manual"],
+    visibility = ["//visibility:private"],
+)

tools/contract-addr/main.go

@@ -0,0 +1,43 @@
+/**
+ * This tool exists to serve currently configured contract address in k8s.
+ * It reads the contract address from a plain text file as provided by etcd.
+ */
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+)
+
+var address = flag.String("address-path", "", "The file path to the plain text file with the contract address")
+
+func main() {
+	flag.Parse()
+	if *address == "" {
+		panic("Contract address filepath not set")
+	}
+
+	fmt.Println("Starting on port 8080")
+
+	if err := http.ListenAndServe(":8080", &handler{}); err != nil {
+		panic("Failed to run server: " + err.Error())
+	}
+}
+
+type handler struct{}
+
+func (h *handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	dat, err := ioutil.ReadFile(*address)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	_, err = io.WriteString(w, string(dat))
+	if err != nil {
+		fmt.Printf("Failed to write response: %v", err)
+	}
+}