Golang implements keepalived

Golang implements Keepalived: a high availability solution

In modern data centers, high availability (HA) is crucial. When a critical network component fails, business continuity can be terminated and result in significant costs or losses. Keepalived is a load balancing and failover software that ensures that the system can still operate normally even if a single component fails. This article will introduce how to implement Keepalived using Golang for high availability solutions.

1. Keepalived Introduction

Keepalived is an open source load balancing software that can ensure the high availability of business in multi-server clusters. When the primary server fails, Keepalived will transfer tasks to the backup server to ensure business continuity. Keepalived uses the VRRP protocol, which allows multiple servers to share a virtual IP address. When the primary server fails, the backup server takes over the virtual IP address and continues to handle client requests, thus ensuring business continuity. In addition to providing failover capabilities, Keepalived also provides health checking, load balancing and other functions.

2. Golang implements Keepalived

Go is a statically typed programming language similar to C. It has the characteristics of high efficiency and high concurrency, and is very popular in network programming, web back-end development and other fields. We can write a simple yet full-featured Keepalived implementation using Golang. In this code example, we will use the net package to handle network connections.

First, we need to define several structures. In order to implement the VRRP protocol, we need to define the following structure:

type VRRPHeader struct {
    ProtoVersion   byte
    Type           byte
    VirtualRouter  byte
    Priority       byte
    CountIPAddr    uint8
    CountAuth      uint8
    AdvertInterval uint16
    Checksum       uint16
    VrrpIpAddr     net.IP
    MasterIpAddr   net.IP
    AuthType       uint8
    AuthDataField  []byte
}

type VRRPMessage struct {
    Header VRRPHeader
    Body   []byte
}

The VRRP protocol header defined by the above structure contains the following fields:

• ProtoVersion: VRRP version number.
• Type: VRRP type (value is 1 or 2).
• VirtualRouter: Virtual router ID.
• Priority: VRRP priority.
• CountIPAddr: The number of IP addresses that record VRRP information.
• CountAuth: Count of authentication data in VRRP messages.
• AdvertInterval: Advert interval (in seconds).
• Checksum: Checksum.
• VrrpIpAddr: virtual IP address.
• MasterIpAddr: Master server IP address.
• AuthType: Authentication type used to authenticate VRRP messages
• AuthDataField: Authentication data in VRRP messages.

The next step is the function that implements the VRRP protocol:

const (
    VRRP_VERSION = 3
    VRRP_TYPE = 1
    VRRP_GROUP_ID = 1
    VRRP_PRIORITY = 100
    ADVERT_INTERVAL = 1
)

func CreateVRRPMessage() VRRPMessage {
    var message VRRPMessage
    message.Header.ProtoVersion = VRRP_VERSION
    message.Header.Type = VRRP_TYPE
    message.Header.VirtualRouter = VRRP_GROUP_ID
    message.Header.Priority = VRRP_PRIORITY
    message.Header.CountIPAddr = 1
    message.Header.CountAuth = 0
    message.Header.AdvertInterval = ADVERT_INTERVAL
    message.Header.Checksum = 0
    message.Header.VrrpIpAddr = net.IPv4(192, 168, 1, 1)
    message.Header.MasterIpAddr = net.IPv4(10, 0, 0, 1)
    message.Header.AuthType = 0

    buf := new(bytes.Buffer)
    binary.Write(buf, binary.BigEndian, message.Header)
    message.Body = buf.Bytes()
    crc := crc32.ChecksumIEEE(message.Body)
    binary.BigEndian.PutUint16(message.Body[6:8], uint16(crc))
    return message
}

func SendVRRPMessage(iface *net.Interface, destIP net.IP, message VRRPMessage) error {
    socket, err := net.DialUDP("udp4", nil, &net.UDPAddr{IP: destIP, Port: 112})
    if err != nil {
        return err
    }
    defer socket.Close()

    addr, err := net.ResolveUDPAddr("udp", iface.Name)
    if err != nil {
        return err
    }

    err = syscall.Bind(socket.FileDescriptor(), addr)
    if err != nil {
        return err
    }

    socket.WriteToUDP(message.Body, &net.UDPAddr{IP: destIP, Port: 112})
    return nil
}

The above code defines a VRRP protocol message structure and a function for sending VRRP messages. You can create a VRRP message using the CreateVRRPMessage function. This initializes various fields of the VRRP protocol header. Use the SendVRRPMessage function to send a VRRP message to a specified IP address. It also requires the name of the interface in order to route packets to the correct network interface.

After completing the above code, we only need to create VRRP messages in the main update loop and send them regularly. Here is a sample program example:

func main() {
    iface, err := net.InterfaceByName("eth0")
    if err != nil {
        fmt.Println("Error getting interface: ", err)
        return
    }

    destIP := net.IPv4(224, 0, 0, 18)

    for {
        message := CreateVRRPMessage()
        err := SendVRRPMessage(iface, destIP, message)
        if err != nil {
            fmt.Println("Error sending VRRP message: ", err)
        }
        time.Sleep(time.Duration(message.Header.AdvertInterval) * time.Second)
    }
}

The above code will send a VRRP message to the 224.0.0.18 address every 1 second. In a real situation, you would need to run this program on multiple servers and make sure they use the same virtual IP address and VRRP priority.

3. Summary

This article introduces how to write a simple Keepalived implementation using Golang. By using the efficient network programming capabilities provided by Golang, we created a high-availability solution capable of failover. Although this is a very simple implementation, it provides a starting point to start understanding how to build a high availability solution.

Using Keepalived can ensure that the business can still run normally even if a single component fails. Monitoring the health of your business, maintaining a failover plan, and responding quickly to failures is critical to help you mitigate the impact when a failure occurs.

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