add nginx-golang-postgres application sample

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/nginx-golang-postgres/backend/Dockerfile

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+FROM golang:1.13-alpine AS build
+WORKDIR /go/src/github.com/org/repo
+COPY . .
+
+RUN go build -o server .
+
+FROM alpine:3.7
+EXPOSE 8000
+COPY --from=build /go/src/github.com/org/repo/server /server
+CMD ["/server"]

samples/nginx-golang-postgres/backend/go.mod

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+module github.com/org/repo
+
+go 1.13
+
+require (
+	github.com/gorilla/context v1.1.1
+	github.com/gorilla/handlers v1.3.0
+	github.com/gorilla/mux v1.6.2
+	github.com/lib/pq v0.0.0-20180327071824-d34b9ff171c2
+)

samples/nginx-golang-postgres/backend/main.go

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+package main
+
+import (
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/gorilla/handlers"
+	"github.com/gorilla/mux"
+	_ "github.com/lib/pq"
+)
+
+func connect() (*sql.DB, error) {
+	bin, err := ioutil.ReadFile("/run/secrets/db-password")
+	if err != nil {
+		return nil, err
+	}
+	return sql.Open("postgres", fmt.Sprintf("postgres://postgres:%s@db:5432/example?sslmode=disable", string(bin)))
+}
+
+func blogHandler(w http.ResponseWriter, r *http.Request) {
+	db, err := connect()
+	if err != nil {
+		w.WriteHeader(500)
+		return
+	}
+	defer db.Close()
+
+	rows, err := db.Query("SELECT title FROM blog")
+	if err != nil {
+		w.WriteHeader(500)
+		return
+	}
+	var titles []string
+	for rows.Next() {
+		var title string
+		err = rows.Scan(&title)
+		titles = append(titles, title)
+	}
+	json.NewEncoder(w).Encode(titles)
+}
+
+func main() {
+	log.Print("Prepare db...")
+	if err := prepare(); err != nil {
+		log.Fatal(err)
+	}
+
+	log.Print("Listening 8000")
+	r := mux.NewRouter()
+	r.HandleFunc("/", blogHandler)
+	log.Fatal(http.ListenAndServe(":8000", handlers.LoggingHandler(os.Stdout, r)))
+}
+
+func prepare() error {
+	db, err := connect()
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+
+	for i := 0; i < 60; i++ {
+		if err := db.Ping(); err == nil {
+			break
+		}
+		time.Sleep(time.Second)
+	}
+
+	if _, err := db.Exec("DROP TABLE IF EXISTS blog"); err != nil {
+		return err
+	}
+
+	if _, err := db.Exec("CREATE TABLE IF NOT EXISTS blog (id SERIAL, title VARCHAR)"); err != nil {
+		return err
+	}
+
+	for i := 0; i < 5; i++ {
+		if _, err := db.Exec("INSERT INTO blog (title) VALUES ($1);", fmt.Sprintf("Blog post #%d", i)); err != nil {
+			return err
+		}
+	}
+	return nil
+}

samples/nginx-golang-postgres/db/password.txt

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+db-frknz

samples/nginx-golang-postgres/docker-compose.yaml

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+version: "3.7"
+services:
+  backend:
+    build: backend
+    secrets:
+    - db-password
+    depends_on:
+    - db
+  db:
+    environment:
+      POSTGRES_DB: example
+      POSTGRES_PASSWORD_FILE: /run/secrets/db-password
+    image: postgres
+    restart: always
+    secrets:
+    - db-password
+    volumes:
+    - db-data:/var/lib/postgresql/data
+  proxy:
+    build: proxy
+    ports:
+    - 80:80
+    depends_on: 
+    - backend
+volumes:
+  db-data: {}
+secrets:
+  db-password:
+    file: db/password.txt

samples/nginx-golang-postgres/proxy/Dockerfile

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+FROM nginx:1.13-alpine
+COPY conf /etc/nginx/conf.d/default.conf

samples/nginx-golang-postgres/proxy/conf

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+server {
+    listen       80;
+    server_name  localhost;
+    location / {
+        proxy_pass   http://backend:8000;
+    }
+
+}