Connecting go and postgres with docker-compose

Question

I'm trying to connect a go and a postgres container with docker-compose.

Here's my docker-compose.yml:

version: '2'
services:
    postgres:
        image: postgres
        ports:
            - "5432"
        environment:
            - POSTGRES_PASSWORD=postgres
    server:
        build: ./server
        command: gin
        volumes:
            - ./server:/go/src/app
        ports:
            - "8080:3000"

At first I was trying with the links command in the docker-compose.yml, but that didn't create any env variables in the server container, so that got me pretty confused. (It's supposed to create SOMETHINGSOMETHING_PORT_5432_TCP_ADDR and SOMETHINGSOMETHING_5432_TCP_PORT, isn't it?)

Then I read somewhere I could just use http://postgres as the host, so I tried that. So now this is how my main.go looks like (NOTE: I'm using Gorp for "ORM"):

func main() {

    dbinfo := fmt.Sprintf("user=%s password=%s host=%s dbname=%s sslmode=disable",
        "postgres",
        os.Getenv("DB_ENV_POSTGRES_PASSWORD"),
        "http://postgres",
        DB_NAME,
    )

    db, err := sql.Open("postgres", dbinfo)

    checkErr(err, "sql.Open failed")


    // construct a gorp DbMap
    dbmap := &gorp.DbMap{Db: db, Dialect: gorp.PostgresDialect{}}

    // add a table, setting the table name to 'posts' and
    // specifying that the Id property is an auto incrementing PK
    dbmap.AddTableWithName(Todo{}, "todos").SetKeys(true, "Id")

    // create the table. in a production system you'd generally
    // use a migration tool, or create the tables via scripts
    err = dbmap.CreateTablesIfNotExists()
    checkErr(err, "Create tables failed")

    http.HandleFunc("/", handler)
    http.ListenAndServe(":3001", nil)
}

Here's a detailed log of docker-compose up (I get connection refused on port 5432):

←[36mserver_1    |←[0m [gin] listening on port 3000
←[33mpostgres_1  |←[0m The files belonging to this database system will be owned by user "postgres".
←[33mpostgres_1  |←[0m This user must also own the server process.
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m The database cluster will be initialized with locale "en_US.utf8".
←[33mpostgres_1  |←[0m The default database encoding has accordingly been set to "UTF8".
←[33mpostgres_1  |←[0m The default text search configuration will be set to "english".
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m Data page checksums are disabled.
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m fixing permissions on existing directory /var/lib/postgresql/data ... ok
←[33mpostgres_1  |←[0m creating subdirectories ... ok
←[33mpostgres_1  |←[0m selecting default max_connections ... 100
←[33mpostgres_1  |←[0m selecting default shared_buffers ... 128MB
←[33mpostgres_1  |←[0m selecting dynamic shared memory implementation ... posix
←[33mpostgres_1  |←[0m creating configuration files ... ok
←[33mpostgres_1  |←[0m creating template1 database in /var/lib/postgresql/data/base/1 ... ok
←[33mpostgres_1  |←[0m initializing pg_authid ... ok
←[33mpostgres_1  |←[0m initializing dependencies ... ok
←[33mpostgres_1  |←[0m creating system views ... ok
←[33mpostgres_1  |←[0m loading system objects' descriptions ... ok
←[33mpostgres_1  |←[0m creating collations ... ok
←[33mpostgres_1  |←[0m creating conversions ... ok
←[33mpostgres_1  |←[0m creating dictionaries ... ok
←[33mpostgres_1  |←[0m setting privileges on built-in objects ... ok
←[33mpostgres_1  |←[0m creating information schema ... ok
←[33mpostgres_1  |←[0m loading PL/pgSQL server-side language ... ok
←[33mpostgres_1  |←[0m vacuuming database template1 ... ok
←[33mpostgres_1  |←[0m copying template1 to template0 ... ok
←[33mpostgres_1  |←[0m copying template1 to postgres ... ok
←[33mpostgres_1  |←[0m syncing data to disk ... ok
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m WARNING: enabling "trust" authentication for local connections
←[33mpostgres_1  |←[0m You can change this by editing pg_hba.conf or using the option -A, or
←[33mpostgres_1  |←[0m --auth-local and --auth-host, the next time you run initdb.
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m Success. You can now start the database server using:
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m     pg_ctl -D /var/lib/postgresql/data -l logfile start
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m waiting for server to start....LOG:  database system was shut down at 2016-08-19 18:31:55 UTC
←[33mpostgres_1  |←[0m LOG:  MultiXact member wraparound protections are now enabled
←[33mpostgres_1  |←[0m LOG:  database system is ready to accept connections
←[33mpostgres_1  |←[0m LOG:  autovacuum launcher started
←[33mpostgres_1  |←[0m  done
←[33mpostgres_1  |←[0m server started
←[33mpostgres_1  |←[0m ALTER ROLE
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m /docker-entrypoint.sh: ignoring /docker-entrypoint-initdb.d/*
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m LOG:  received fast shutdown request
←[33mpostgres_1  |←[0m LOG:  aborting any active transactions
←[33mpostgres_1  |←[0m LOG:  autovacuum launcher shutting down
←[33mpostgres_1  |←[0m LOG:  shutting down
←[33mpostgres_1  |←[0m waiting for server to shut down....LOG:  database system is shut down
←[33mpostgres_1  |←[0m  done
←[33mpostgres_1  |←[0m server stopped
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m PostgreSQL init process complete; ready for start up.
←[33mpostgres_1  |←[0m
←[33mpostgres_1  |←[0m LOG:  database system was shut down at 2016-08-19 18:31:57 UTC
←[33mpostgres_1  |←[0m LOG:  MultiXact member wraparound protections are now enabled
←[33mpostgres_1  |←[0m LOG:  database system is ready to accept connections
←[33mpostgres_1  |←[0m LOG:  autovacuum launcher started
←[36mserver_1    |←[0m 2016/08/19 18:32:05 Create tables failed dial tcp [::1]:5432: getsockopt: connection refused
←[36mserver_1    |←[0m 2016/08/19 18:32:05 http: proxy error: dial tcp [::1]:3001: getsockopt: connection refused
←[36mserver_1    |←[0m 2016/08/19 18:32:05 Create tables failed dial tcp [::1]:5432: getsockopt: connection refused
←[36mserver_1    |←[0m 2016/08/19 18:32:05 http: proxy error: dial tcp [::1]:3001: getsockopt: connection refused

So my question is how do I get these to be able to talk to each other and what exactly am I doing wrong here?

Answer 1

That a docker networking question.You can read more about it here. Docker dns does all the hard work, so you can reach each container by the name you gave it on the compose file.

Posgres url usually works like

postgresql://user:password@ip:port/database

So for you, it would be something like.

db, err := sql.Open("postgres", "postgresql://user:password@postgres/mydatabase)

Note that you do not need the port if postgres is on the standard port (5432).