I'm new to Docker. This project is just for my own understanding. It's likely that I use incorrect terminology and/or am more confused than I think I am. Corrections are gratefully accepted.
I'm using two docker images: the official postgres image and my own Go app and Dockerfile. Using docker-compose up I get the connection refused error.
I think that there are potentially two different problems:
One, the database is not running when the app is trying to connect.
Two, the app is simply using an invalid IP.
I have app code that should be giving the database time to start up to address the first potential problem (see code below). Judging by the error message, I don't think I'm even getting that far.
I have two services: db-access (that's the Go app) and postgres-db.
I have tried using these host names in the app connection string:
"localhost",
"postgres-db" (as it's named in the docker-compose.yml),
"0.0.0.0".
Using the postgres-db as the hostname:
The app container is trying: dial tcp 172.22.0.2:5432.
Postgres is saying: listening on IPv4 address "0.0.0.0", port 5432.
In the docker-compose.yml I have tried using these statements:
depends_on:
- postgres-db
and
links:
- postgres-db
I have tried reversing the order of the services in the docker-compose.yml but they appear to start up in the same order either way.
When I run the postgres container and the Go app separately I get the expected behavior. To run them separately I'm using these commands:
docker run --rm --name postgres-db -e POSTGRES_PASSWORD=docker -d -p 5432:5432 -v /Users/ForeignFood/Development/go/src/github.com/skillitzimberg/docker/volumes/postgres:/var/lib/postgresql/data postgres
followed by
go run basicapi
I can also run docker-compose up, which gives the connection refused error, then ctrl+C, then run go run basicapi and get the expected behavior.
Here are the project files . . .
main.go:
package main
import (
"basicapi/models"
"fmt"
"net/http"
_ "github.com/lib/pq"
)
const (
host = "postgres-db"
port = 5432
user = "postgres"
password = "docker"
dbname = "myfirstdb"
)
var psqlDatabaseConnectionString = fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
host, port, user, password, dbname)
func main() {
models.InitDB(psqlDatabaseConnectionString)
http.HandleFunc("/users", usersList)
http.ListenAndServe(":3000", nil)
}
func usersList(w http.ResponseWriter, r *http.Request) {
if r.Method != "GET" {
http.Error(w, http.StatusText(405), 405)
return
}
usrs, err := models.AllUsers()
if err != nil {
fmt.Println(err)
http.Error(w, http.StatusText(500), 500)
return
}
for _, usr := range usrs {
fmt.Fprintf(w, "%d, %s, %s, %.s
", usr.ID, usr.FirstName, usr.LastName, usr.Email)
}
}
models/db.go:
package models
import (
"database/sql"
"fmt"
"log"
"time"
_ "github.com/lib/pq"
)
var db *sql.DB
func InitDB(dataSourceName string) {
var err error
for i := 0; i < 10; i++ {
db, err = sql.Open("postgres", dataSourceName)
if err != nil {
fmt.Println(i)
fmt.Println(err)
time.Sleep(time.Second * 10)
}
}
if err != nil {
log.Panic(err)
}
if err = db.Ping(); err != nil {
log.Panic(err)
}
fmt.Printf("Connection to database successful!
")
}
models/users.go:
package models
import "fmt"
type User struct {
ID int
Age int
FirstName string
LastName string
Email string
}
func AllUsers() ([]*User, error) {
fmt.Println("Got to AllUsers")
rows, err := db.Query("SELECT * FROM users")
if err != nil {
fmt.Println(err)
return nil, err
}
defer rows.Close()
users := make([]*User, 0)
for rows.Next() {
user := new(User)
err := rows.Scan(&user.ID, &user.Age, &user.FirstName, &user.LastName, &user.Email)
if err != nil {
return nil, err
}
users = append(users, user)
}
if err = rows.Err(); err != nil {
return nil, err
}
return users, nil
}
Dockerfile:
FROM golang
WORKDIR /app
COPY ./go.mod ./go.mod
COPY ./go.sum ./go.sum
RUN go mod download
COPY . .
RUN go build -o /bin/app
CMD [ "app" ]
docker-compose.yml
services:
db-access:
build: .
depends_on:
- postgres-db
ports:
- "3000:3000"
postgres-db:
image: postgres
volumes:
- /Users/ForeignFood/Development/go/src/github.com/skillitzimberg/docker/volumes/postgres:/var/lib/postgresql/data
ports:
- "5432:5432"
environment:
POSTGRES_USER: "postgres"
POSTGRES_PASSWORD: "docker"
POSTGRES_DATABASE: "myfirstdb"
Expected results: Navigating to localhost:3000/users shows:
1, Someone, Alastname,
2, SomeoneElse, AnotherLastName,
etc...
Actual results:
browser:
This site can't be reachedterminal:
~/ >> docker-compose up
Starting basicapi_postgres-db_1 ... done
Starting basicapi_db-access_1 ... done
Attaching to basicapi_postgres-db_1, basicapi_db-access_1
db-access_1 | 2019/05/17 16:53:54 dial tcp 172.22.0.2:5432: connect: connection refused
db-access_1 | panic: dial tcp 172.22.0.2:5432: connect: connection refused
db-access_1 |
db-access_1 | goroutine 1 [running]:
db-access_1 | log.Panic(0xc0000c3f40, 0x1, 0x1)
db-access_1 | /usr/local/go/src/log/log.go:333 +0xac
db-access_1 | basicapi/models.InitDB(0xc000062120, 0x55)
db-access_1 | /app/models/db.go:30 +0x27c
db-access_1 | main.main()
db-access_1 | /app/main.go:23 +0x3d
basicapi_db-access_1 exited with code 2
postgres-db_1 | 2019-05-17 16:53:58.770 UTC [1] LOG: listening on IPv4 address "0.0.0.0", port 5432
postgres-db_1 | 2019-05-17 16:53:58.770 UTC [1] LOG: listening on IPv6 address "::", port 5432
postgres-db_1 | 2019-05-17 16:53:58.776 UTC [1] LOG: listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
postgres-db_1 | 2019-05-17 16:53:58.905 UTC [22] LOG: database system was shut down at 2019-05-17 16:53:23 UTC
postgres-db_1 | 2019-05-17 16:53:58.952 UTC [1] LOG: database system is ready to accept connections
Thank you for any insights.
