When running Apache Bench (ab) on macOS to test a local Elasticsearch instance at http://localhost:9202, developers often encounter the cryptic error:

apr_socket_connect(): Invalid argument (22)

This typically occurs when ab attempts to establish a TCP connection but fails due to misconfigured networking parameters.

The error stems from macOS's specific handling of IPv6 and localhost resolution. The APR (Apache Portable Runtime) library used by ab gets confused when:

• DNS resolution returns both IPv4 and IPv6 addresses for localhost
• The target port isn't properly specified in the connection attempt
• Network stack receives malformed socket parameters

Here are three proven methods to resolve this issue:

Method 1: Force IPv4 resolution

ab -n 100 -c 10 http://127.0.0.1:9202/

Using the explicit IPv4 loopback address bypasses IPv6 resolution issues entirely.

Method 2: Update your ab version

brew update && brew upgrade ab

Newer versions of Apache Bench handle dual-stack sockets more gracefully.

Method 3: Modify hosts file

# Edit /etc/hosts
::1             localhost
127.0.0.1       localhost

For persistent cases, try these diagnostic commands:

# Check port accessibility
nc -zv localhost 9202

# Verify DNS resolution
dig localhost

# Test with curl for comparison
curl -v http://localhost:9202

If the issue persists across tools, examine your Elasticsearch network binding configuration in elasticsearch.yml:

network.host: 0.0.0.0
http.port: 9202

When ab proves problematic, consider these alternatives:

• wrk: Modern HTTP benchmarking tool
• siege: Advanced load testing
• hey: Golang-based ab alternative

Example with hey:

hey -n 100 -c 10 http://localhost:9202

---

When running Apache Bench (ab) on macOS to test endpoints like http://localhost:9202, you might encounter:

apr_socket_connect(): Invalid argument (22)

This typically indicates a socket connection issue, often related to DNS resolution, port configuration, or IPv6/IPv4 handling.

Here are frequent cases where this occurs:

• Testing localhost with explicit port numbers
• Using hostnames instead of IP addresses
• IPv6 misconfiguration in modern macOS versions

Solution 1: Force IPv4

ab -n 100 -c 10 http://127.0.0.1:9202/

Replace localhost with 127.0.0.1 to bypass IPv6 resolution.

Solution 2: Check Port Availability

lsof -i :9202
netstat -an | grep 9202

For persistent cases, enable verbose logging:

ab -v 4 -n 1 http://localhost:9202

Sample output analysis:

LOG: open socket: Invalid argument (22)
LOG: Connect to localhost:9202 failed

Edit /etc/hosts to ensure proper resolution:

127.0.0.1       localhost
::1             localhost

If issues persist, consider:

brew install wrk
wrk -t4 -c100 -d10s http://localhost:9202