Configure WebSocket Support

You can configure an ALB to support WebSockets, a communication protocol that provides full-duplex communication channels over a single TCP connection.

To configure WebSocket support follow these steps:

1. Set up an ALB either using the DCD or using the following API POST request.

curl -X POST -H ‘application/json’ -H ‘Authorization: Bearer ...’  https://api.ionos.com/cloudapi/v6/datacenters/{datacenterId}/applicationloadbalancers -d’
{
  “properties”: {
    “name”: “alb-websocket”,
    “listenerLan”: 1,
    “targetLan”: 2,
    “ips”: [“1.1.1.1”],
    “lbPrivateIps”: [“10.20.30.40/24”]
}

1. Create a Target Group.

2. Before setting up an ALB, predefine a target group to distribute the incoming traffic to the correct target. An IP address and a port are used to register a target.

3. Ensure that no HTTP health check is configured for the target group for WebSocket support. Otherwise the ALB targets will be unavailable for load balancing. TCP health checks (healthCheckEnabled) are allowed.

4. You can either create target group using the Create a Target Group or the following POST request.

curl -X POST -H ‘application/json’ -H ‘Authorization: Bearer ...’  https://api.ionos.com/cloudapi/v6/targetgroups
{
  “properties”: {
    “name”: “websocket-target-group”,
    “algorithm”: “ROUND_ROBIN”,
    “protocol”: “HTTP”,
    “targets”: [
      {
        “ip”: “10.20.30.100”,
        “port”: 8080,
        “weight”: 10,
        “healthCheckEnabled”: true
      }
    ]
}

1. Create a Forwarding rule.

Forwarding rules define how client traffic is distributed to the targets. More than one rule can be created for the same load balancer.

Forwarding rule example:

{
  “properties”: {
    “name”: “websocket-rule”,
    “protocol”: “HTTP”,
    “listenerIp”: “1.2.3.4”,
    “listenerPort”: 80,
    “httpRules”: [
      {
        “name”: “forward”,
        “type”: “FORWARD”,
        “targetGroup”: “<target group id>”
      }
    ]
}

Note: Web Socket traffic differs from standard HTTP traffic, so ensure that your HTTP rules or conditions are accurate. Only the initial protocol upgrade to enable Web Socket tunneling can be targeted by the HTTP rule conditions. An example of this:

{
 “httpRules”: [
      {
        “name”: “forward”,
        “type”: “FORWARD”,
        “targetGroup”: “<target group ID>“,
        “conditions”: [
          {
            “type”: “HEADER”,
            “condition”: “EQUALS”,
            “key”: “Connection”,
            “value”: “upgrade”
          },
          {
            “type”: “HEADER”,
            “condition”: “EQUALS”,
            “key”: “Upgrade”,
            “value”: “websocket”
          }
        ]
      }
    ]
}

Result: The ALB can now handle HTTP protocol upgrade requests to switch to Web Socket tunneling.