如何在 Docker Compose 多容器应用程序中使用 GoCQL 连接到

Question

我正在尝试构建一个使用用户名和密码身份验证连接到 Cassandra 的应用程序的简化示例。为此，我改编了docker-compose.yml来自https://hub.docker.com/r/bitnami/cassandra/的内容，如下所示：version: '2'services:  cassandra:    image: 'docker.io/bitnami/cassandra:3-debian-10'    ports:      - '7000:7000'      - '9042:9042'    volumes:      - 'cassandra_data:/bitnami'    environment:      - CASSANDRA_SEEDS=cassandra      - CASSANDRA_PASSWORD_SEEDER=yes      - CASSANDRA_PASSWORD=cassandra  backend:    build: .    environment:      - CASSANDRA_USERNAME=cassandra      - CASSANDRA_PASSWORD=cassandravolumes:  cassandra_data:    driver: local我的目录结构在哪里.├── Dockerfile├── docker-compose.yml├── go.mod├── go.sum└── main.go多阶段Dockerfile是FROM golang AS builderWORKDIR /go/src/app/COPY . .RUN GO111MODULE=on CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .FROM alpine:latest  RUN apk --no-cache add ca-certificatesWORKDIR /root/COPY --from=builder /go/src/app/app .CMD ["./app"]  并main.go尝试使用以下命令创建 Cassandra 会话gocql：package mainimport (    "log"    "os"    "github.com/gocql/gocql")func main() {    cluster := gocql.NewCluster("cassandra")    cluster.Authenticator = gocql.PasswordAuthenticator{        Username: os.Getenv("CASSANDRA_USERNAME"),        Password: os.Getenv("CASSANDRA_PASSWORD"),    }    if _, err := cluster.CreateSession(); err != nil {        log.Fatalf("CreateSession: %v", err)    }}用户名和密码都已设置为“cassandra”的默认值，如https://hub.docker.com/r/bitnami/cassandra/中的“连接到其他容器”示例中所示。问题是，如果我尝试使用docker-compose build后跟运行这个多容器应用程序docker-compose up，我会收到以下错误：backend_1    | 2020/11/04 15:10:34 CreateSession: gocql: unable to create session: unable to discover protocol version: dial tcp 172.18.0.3:9042: connect: connection refused我不明白这里出了什么问题：主机名、端口号、用户名和密码似乎都正确。任何想法为什么连接被拒绝？

Answer 1

Cassandra 需要几秒钟来启动并开始接受连接；backend在准备好之前尝试连接。如果您backend在一小段延迟后启动（使用），您的配置工作正常（对我来说docker-compose start backend）。修改backend以重试连接对我来说可靠，即

for {

    _, err := cluster.CreateSession()

    if  err == nil {

        break

    }

    log.Printf("CreateSession: %v", err)

    time.Sleep(time.Second)

}

log.Printf("Connected OK")

日志：

backend_1    | 2020/11/04 17:53:23 CreateSession: gocql: unable to create session: unable to discover protocol version: dial tcp 172.26.0.2:9042: connect: connection refused

backend_1    | 2020/11/04 17:53:24 CreateSession: gocql: unable to create session: unable to discover protocol version: dial tcp 172.26.0.2:9042: connect: connection refused

.......

backend_1    | 2020/11/04 17:53:36 CreateSession: gocql: unable to create session: unable to discover protocol version: dial tcp 172.26.0.2:9042: connect: connection refused

backend_1    | 2020/11/04 17:53:37 Connected OK