opcache preloading does not exist yet, and here is what does

Preloading arrives in 7.4 and this year the closest equivalent is making sure the cache is warm before traffic reaches a new release, which is a deployment concern rather than a configuration one.

#!/usr/bin/env bash
set -euo pipefail

systemctl reload php7.2-fpm

# warm the pool before the load balancer sends real traffic
for path in / /products /checkout; do
    curl -fsS -o /dev/null "http://127.0.0.1${path}"
done

# then, and only then, mark the node healthy

The first request after a reload compiles everything it touches, and on a large framework that is several hundred milliseconds — which the first real user pays. Hitting three representative URLs locally before the health check passes moves that cost off the critical path. On a single server without a load balancer the same idea applies with less ceremony, and it still removes the slow first request that everyone has seen and nobody investigates.