Redis – Cannot connect to Mongo Atlas Cloud in Docker Compose: incomplete read of message header & certificate error

I have a Go app that does basic CRUD operations and uses MongoDB for data persistence.

I am using Mongo Atlas connection string to connect the app to MongoDB and things work fine when I run the application on my local dev machine. But when I push everything to a docker container, in a docker-compose workflow, I start getting this error:

server selection error: server selection timeout, current topology: { Type: ReplicaSetNoPrimary, Servers: [{ Addr: app-test-shard-00-00-zfzs6.mongodb.net:27017, Type: Unknown, State: Connected, Average RTT: 0, Last error: connection() : x509: certificate signed by unknown authority }, { Addr: app-test-shard-00-01-zfzs6.mongodb.net:27017, Type: Unknown, State: Connected, Average RTT: 0, Last error: connection() : x509: certificate signed by unknown authority }, { Addr: app-test-shard-00-02-zfzs6.mongodb.net:27017, Type: Unknown, State: Connected, Average RTT: 0, Last error: connection() : x509: certificate signed by unknown authority }, ] }

This is how my docker-compose.yml looks:

services: 
redis:
    image: redis
    restart: always
app:
    image: docker.pkg.github.com/<user>/<project>/<image>:latest
    ports: 
        - 80:8080
    environment: 
        - APP_ENV=docker
        - GIN_MODE=release
    depends_on: 
        - redis
    restart: on-failure

This is how my connection string looks:
mongodb://user:[email protected]:27017,app-test-shard-00-01-zfzs6.mongodb.net:27017,app-test-shard-00-02-zfzs6.mongodb.net:27017/test?ssl=true&replicaSet=app-test-shard-0&authSource=admin&retryWrites=true&w=majority

I have checked this question and a couple of others, but none seem to fix this.

I also checked docker’s networking config, I am using a bridge driver, which should allow access to outside apps (i.e. Mongo Atlas)

Go Version: 1.13

Mongo Driver: mongodb/mongo-go-driver v1.2.0

Dockerfile:

FROM golang:alpine as builder
WORKDIR /build
COPY . .
RUN apk add git openssh build-base
RUN git config --global url."[email protected]:".insteadOf "https://github.com/"
COPY keys/id_rsa /root/.ssh/id_rsa
RUN chmod 600 /root/.ssh/id_rsa
RUN ssh-keyscan -t rsa github.com >> /root/.ssh/known_hosts
ENV GOPRIVATE=github.com/contributor-org
RUN go build

FROM alpine
WORKDIR /org
COPY --from=builder /build/app .
COPY config/*.yml config/
RUN mkdir -p /var/log
CMD ["./app"]

DB Connection code:

type databaseClient struct { // Implements the Database interface
    collection *mongo.Collection
}

func GetNewClient(cfg *config.Config, log *logger.Logger) (Database, error) {
    clientOptions := options.Client().ApplyURI(cfg.Database.ConnectionString)
    client, err := mongo.NewClient(clientOptions)
    if err != nil {
        log.Errorln(err)
    }
    err = client.Connect(context.Background())

    if err != nil {
        log.Fatalln("Failed to connect to Mongo!", err)
        return nil, err
    }

    log.Info("Connected to Mongo!")

    db := client.Database(cfg.Database.Database)
    if db == nil {
        err := fmt.Errorf("DB (%s) not found", cfg.Database)
        log.Error(err)
        return nil, err
    }
    collection := db.Collection(cfg.Database.Collection)
    if collection == nil {
        err := fmt.Errorf("Collection (%s) not found on DB (%s)", cfg.Database.Collection, cfg.Database.Database)
        log.Error(err)
        return nil, err
    }
    return &databaseClient{collection: collection}, nil
}

DB Interface:

type Database interface {
    GetByBookname(context.Context, string) (*model.Book, error)
    GetOneByFilter(context.Context, map[string]interface{}) (*model.Book, error)
    GetAll(context.Context) ([]*model.Book, error)
    GetAllByFilters(context.Context, map[string]interface{}) ([]*model.Book, error)
    AddBook(context.Context, *model.Book) (string, error)
    UpdateBook(context.Context, string, map[string]interface{}) (*model.Book, error)
    DeactivateBook(context.Context, string) error
    OverwriteBook(context.Context, string, *model.Book) (*model.Book, error)
    OnboardBook(*model.Book, string, bool) (string, error)
}