When managing thousands of virtual hosts in Nginx, the server_names_hash parameters become critical performance factors. The default values (max_size=256, bucket_size=64) work fine for small deployments but fail spectacularly when scaling beyond 30-50 domains, as seen in your error logs.

Nginx uses hash tables for rapid server_name lookups. Each bucket contains a linked list of server names - longer lists degrade performance. The relationship between parameters:

# Formula for estimating required bucket_size
bucket_size = longest_domain_length + 32
# max_size should be total_domains * 1.5 (safety margin)

For your 200-domain setup (with planned growth):

http {
    server_names_hash_bucket_size 128;  # For domains up to 96 chars
    server_names_hash_max_size 2048;    # Supports ~1500 domains
    
    # Additional performance tweaks
    server_names_hash_max_slots 32768;  # Available in Nginx 1.15.9+
    resolver_timeout 30s;
}

The lengthy reload times indicate two issues:

1. Hash table rebuilding overhead
2. Configuration parsing latency

Implement these improvements:

# In main nginx.conf
worker_processes auto;  # Match CPU cores
worker_rlimit_nofile 100000;  # Handle more connections

events {
    worker_connections 4096;
    use epoll;  # For Linux systems
    multi_accept on;
}

For 10,000+ domains, consider:

# Wildcard-based approach (reduces hash table entries)
server {
    listen 80;
    server_name ~^(?.+)\.domain\.com$;
    location / {
        proxy_pass http://127.0.0.1:8011;
        proxy_set_header Host $host;
    }
}

Combine with Lua scripting for dynamic SSL certificates:

server {
    listen 443 ssl;
    ssl_certificate_by_lua_block {
        local ssl = require "ngx.ssl"
        -- Dynamic certificate loading logic here
    }
}

Add these to your monitoring:

# Check hash table stats
nginx -T 2>&1 | grep -A 5 "server names hash"

# Sample log format for tracking
log_format vhost '$host $remote_addr [$time_local] '
                 '"$request" $status $body_bytes_sent';

When managing hundreds or thousands of virtual hosts in Nginx, the server_names_hash parameters become critical for performance. The default values (bucket_size=64, max_size=512) work fine for small setups, but when you're hosting a multi-tenant platform where each user gets their own subdomain or custom domain, these defaults quickly become inadequate.

Nginx uses hash tables for fast server_name matching during request processing. The system has two key controls:

server_names_hash_bucket_size 64;  # Size of each hash bucket (must be power of 2)
server_names_hash_max_size 1024;   # Maximum number of server names

Each virtual host's server_name gets hashed and placed in a bucket. When buckets become too full (due to hash collisions), Nginx needs to rebuild the hash table with larger parameters.

For a system with thousands of domains, I recommend these settings:

server_names_hash_bucket_size 128;
server_names_hash_max_size 8192;

The bucket size should be:

• Minimum: Longest server_name length (including wildcards)
• Optimal: Next power of 2 above that length

With 2000+ domains, you'll notice:

# Before optimization
nginx -t   # Takes 3-5 seconds
service nginx reload   # Causes 2-3 second downtime

# After optimization
nginx -t -T /dev/shm/nginx_temp.conf   # Test config in RAM
service nginx reload   # Downtime reduced to under 1 second

For truly massive deployments (10,000+ domains):

# In main nginx.conf
server_names_hash_bucket_size 256;
server_names_hash_max_size 32768;

# Enable shared memory for hash tables
proxy_cache_path /dev/shm/nginx_cache levels=1:2 keys_zone=my_cache:128m;

worker_processes auto;
worker_rlimit_nofile 100000;

Create a monitoring script to check hash table usage:

#!/bin/bash
DOMAIN_COUNT=$(grep -r "server_name" /etc/nginx/conf.d/ | wc -l)
BUCKET_SIZE=$(nginx -T 2>&1 | grep server_names_hash_bucket_size | awk '{print $2}')
echo "Domains: $DOMAIN_COUNT | Current bucket size: $BUCKET_SIZE"