Why Does My Golang mgo Connection to MongoDB Atlas Keep Failing with a \'No Reachable Server\' Error?

Connecting to MongoDB Atlas using Golang mgo: Persistent "no reachable server" to replica set

This error message commonly arises when attempting to connect to a MongoDB Atlas replica set using Golang's mgo driver. To resolve this issue, consider the following steps:

Utilizing the mgo code snippet provided below:

import (
    "gopkg.in/mgo.v2"
    "crypto/tls"
    "net"
)

// Configure TLS settings
tlsConfig := &tls.Config{}

// Initialize the DialInfo object
dialInfo := &mgo.DialInfo{
    Addrs: []string{"prefix1.mongodb.net:27017", 
                    "prefix2.mongodb.net:27017",
                    "prefix3.mongodb.net:27017"},
    Database: "authDatabaseName",
    Username: "user",
    Password: "pass",
}

// Override the default DialServer method
dialInfo.DialServer = func(addr *mgo.ServerAddr) (net.Conn, error) {
    conn, err := tls.Dial("tcp", addr.String(), tlsConfig)
    return conn, err
}

// Establish the connection using DialWithInfo
session, err := mgo.DialWithInfo(dialInfo)

Keep in mind that specifying a single replica set member as a seed is an equally valid option:

Addrs: []string{"prefix2.mongodb.net:27017"}

For further insights, refer to the following resources:

• [tls.Dial()](https://golang.org/pkg/crypto/tls/#Dial)
• [DialInfo](https://godoc.org/gopkg.in/mgo.v2#DialInfo)
• [DialWithInfo](https://godoc.org/gopkg.in/mgo.v2#DialWithInfo)

Update:

Alternatively, the mgo.ParseURL() method can be employed to interpret the MongoDB Atlas URI string. However, it currently lacks support for SSL.

As a workaround, you can remove the ssl=true parameter before parsing:

// URI without ssl=true
var mongoURI = "mongodb://username:[email protected],prefix2.mongodb.net,prefix3.mongodb.net/dbName?replicaSet=replName&authSource=admin"

dialInfo, err := mgo.ParseURL(mongoURI)

// Subsequent code remains similar to the previous example.

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