When browsers receive multiple A records from a DNS response (DNS Round Robin), their behavior isn't standardized but follows common implementation patterns:

• Chrome/Chromium: Uses the first IP initially, sticks to it while responsive (2-3 minute timeout), then cycles through alternatives
• Firefox: Similar stickiness but with faster failover (30-60 second detection)
• Safari: Most aggressive at switching between IPs, sometimes even during active connections

Browsers rely on the OS's TCP stack behavior. Most operating systems will:

// Typical connection attempt pseudocode
function connectWithFallback(hostname, ips, port=443) {
  for (ip of ips) {
    try {
      socket = new Socket(ip, port, {timeout: 3000});
      return socket; // First successful connection
    } catch (e) {
      continue; // Try next IP
    }
  }
  throw new Error("All IPs failed");
}

The DNS Time-To-Live (TTL) value significantly impacts behavior:

To verify your specific browser's behavior:

// Node.js test server
const http = require('http');
const servers = [
  { ip: '192.0.2.1', port: 3000, isUp: true },
  { ip: '192.0.2.2', port: 3000, isUp: true }
];

servers.forEach(server => {
  http.createServer((req, res) => {
    console.log(Request served by ${server.ip});
    res.end(Hello from ${server.ip}\n);
  }).listen(server.port, server.ip);
});

// Randomly take servers down every 2 minutes
setInterval(() => {
  const target = Math.floor(Math.random() * servers.length);
  servers[target].isUp = !servers[target].isUp;
  console.log(${servers[target].ip} is now ${servers[target].isUp ? 'UP' : 'DOWN'});
}, 120000);

For more reliable failover than DNS RR:

• HTTP 307 Redirects: Application-level control
• Anycast Routing: Network-layer solution
• Cloud Load Balancers: AWS ALB, GCP LB, etc.

Recent versions show these characteristics:

• Chrome 90+: Implemented "Happy Eyeballs" algorithm for IPv4/IPv6
• Firefox 85+: More aggressive DNS prefetching affects RR behavior
• Edge: Similar to Chrome but with different timeout thresholds

When multiple A-records are returned in a DNS response, browser behavior varies significantly across implementations. Modern browsers generally exhibit one of these patterns:

• Sticky IP Selection: Chrome and Firefox tend to stick with the initially selected IP for the duration of the TCP connection or browser session
• Rotating Selection: Some mobile browsers may rotate through IPs more aggressively
• Failover Behavior: Most will switch only when the current IP becomes unreachable

You can verify this behavior using simple DNS configuration and curl commands:

# Sample DNS zone file configuration
example.com.    IN  A   192.0.2.1
example.com.    IN  A   192.0.2.2
example.com.    IN  A   192.0.2.3

# Test with curl (Linux/macOS)
for i in {1..10}; do
  curl -v http://example.com 2>&1 | grep "Trying"
  sleep 1
done

Mainstream browsers implement different connection management strategies:

DNS Round Robin can work as a basic failover mechanism if:

1. Your clients primarily use Chrome/Firefox
2. Downtime detection is handled quickly
3. Session persistence isn't critical

However, for production systems, consider these more robust alternatives:

# Nginx upstream configuration example
upstream backend {
  server backend1.example.com:80;
  server backend2.example.com:80 backup;
  server backend3.example.com:80 backup;
}

For more sophisticated DNS-based solutions, consider these approaches:

• DNS-based geolocation routing
• Weighted Round Robin (WRR) records
• EDNS Client Subnet (ECS) aware DNS

Example using AWS Route 53 latency-based routing:

{
  "AliasTarget": {
    "HostedZoneId": "Z2FDTNDATAQYW2",
    "DNSName": "example.com",
    "EvaluateTargetHealth": true
  }
}