无法从api-service连接到docker容器内的db主机，以便在golang中使用goose进行迁移

Question

goose是帮助我运行所有*sql文件并在数据库中运行查询的迁移工具。我想在我的api服务上的docker容器中使用这个工具自动迁移(创建表和其他东西)。问题是当docker运行命令"goose run“时，它会收到一个错误-goose run: dial tcp: lookup db on 192.168.63.6:53: no The host。

docker-compose

services:
  db:
    build: ./db
    volumes:
      - ./db/pgdata:/pgdata
    image: postgres
    ports:
      - "5432"
    restart: always
    environment:
      - POSTGRES_USER=user
      - POSTGRES_DB=dbname
      - POSTGRES_PASSWORD=123
      - PGDATA=/pgdata

  api:
    build:
      context: ./api
    restart: always
    volumes:
      - ./api:/go/src/github.com/gitlees/todoapp/api
    ports:
      - "5000:8080"
    links: 
      - "db"

Dockerfile接口

RUN go get -u github.com/pressly/goose/cmd/goose

RUN goose postgres "host=db user=user dbname=dbname sslmode=disable password=123" up

Answer 1

首先，让我们更深入地了解一下Dockerfile。我也设置了一个repository for demo purposes for this question。

# We use a so called two stage build.
# Basically this means we build our go binary in one image
# which has the go compiler and all the required tools and libraries.
# However, since we do not need those in our production image,
# we copy the binary created into a basic alpine image
# resulting in a much smaller image for production.

# We define our image for the build environment...
FROM golang:1.11-alpine3.8 as build

# ...and copy our project directory tp the according place.
COPY . "/go/src/github.com/mwmahlberg/so-postgres-compose"
# We set our work directory...
WORKDIR /go/src/github.com/mwmahlberg/so-postgres-compose
# ...and add git, which - forever reason, is not included into the golang image.
RUN apk add git

# We set up our dependency management and make sure all dependencies outside
# the standard library are installed.
RUN set -x && \
    go get github.com/golang/dep/cmd/dep && \
    dep ensure -v
# Finally, we build our binary and name it accordingly    
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /apiserver

# Now for the second stage, we use a basic alpine image...
FROM alpine:3.8
# ... update it...
RUN apk --no-cache upgrade
# .. and take the binary from the image we build above.
# Note the location: [/usr]{/bin:/sbin} are reserved for
# the OS's package manager. Binaries added to an OS by
# the administrator which are not part of the OS's package
# mangement system should always go below /usr/local/{bin,sbin}
COPY --from=build /apiserver /usr/local/bin/apiserver
# Last but not least, we tell docker which binary to execute.
ENTRYPOINT ["/usr/local/bin/apiserver"]

最后一行实际上应该可以做到这一点：ENTRYPOINT指定在启动容器时要执行的命令。参数将附加到此命令。因此，要添加连接字符串，可以执行以下操作

api:
  build: .
  restart: always
  command: "host=db user=user dbname=dbname sslmode=disable password=123"
  ports:
    - 8080:8080
  links:
    - db

您应该做的最后一件事是对docker镜像进行静态配置，如您在示例中所示。您基本上设置了一个静态连接字符串，这剥夺了您使用容器的大部分灵活性。

然而，imho首先使用命令行标志来配置容器是不好的做法。一种更灵活的方法是使用环境变量。例如，在kubernetes中，您可以使用use a config map来设置环境变量，这些变量依次配置一个pod。但是，环境变量也可以与docker-compose或docker swarm一起使用。

因此，我会将docker-compose.yml更改为如下所示：

version: '3'
services:
  db:
    volumes:
      - ./db/pgdata:/pgdata
    image: postgres
    ports:
      - "5432"
    restart: always
    environment:
      - POSTGRES_USER=user
      - POSTGRES_DB=dbname
      - POSTGRES_PASSWORD=123
      - PGDATA=/pgdata

  # adminer added for convenience
  adminer:
    image: adminer
    restart: always
    ports:
      - 8081:8080
    depends_on:
      - db

  api:
    build: .
    restart: always
    ports:
      - 8080:8080
    depends_on:
      - db
    environment:
      - POSTGRES_USER=user
      - POSTGRES_DB=dbname
      - POSTGRES_PASSWORD=123
      - POSTGRES_HOST=db
      - POSTGRES_PORT=5432    

并使用环境变量配置二进制文件。

我在存储库中添加了一个simple example how to use environment variables in Go。请注意，像https://github.com/spf13/cobra/cobra或https://gopkg.in/alecthomas/kingpin.v2这样的项目使得使用环境变量变得更加容易，因为它们提供了自动类型转换、轻松设置默认值等功能。

至于更深入地解释为什么要使用环境变量，您可能需要阅读part 3 of the 12 factor app methodology。

hth

Answer 2

运行命令在构建阶段执行。在此阶段，还没有容器。

用于连接到其他容器的命令应该在Dockerfile中的CMD或ENTRYPOINT中定义。