Derive RoadRunner worker defaults from the container CPU limit

docker/docker-entrypoint.sh

@@ -26,6 +26,34 @@ fi
 php vendor/bin/shlink-installer init ${flags}
 
 if [ "$SHLINK_RUNTIME" = 'rr' ]; then
+  # RoadRunner resolves `num_workers: 0` against the number of CPUs the HOST
+  # reports, which is unaffected by any CPU limit set on the container. On a
+  # many-core host that starts dozens of workers which can never run
+  # concurrently, at roughly 50-60MB each, so the container idles far above the
+  # memory it needs and is eventually killed under load.
+  #
+  # When the container has a CPU limit, derive the defaults from that instead.
+  # Without a limit, nothing changes.
+  container_cpus=''
+  if [ -r /sys/fs/cgroup/cpu.max ]; then                 # cgroup v2
+    read -r cpu_quota cpu_period < /sys/fs/cgroup/cpu.max
+  elif [ -r /sys/fs/cgroup/cpu/cpu.cfs_quota_us ]; then  # cgroup v1
+    cpu_quota=$(cat /sys/fs/cgroup/cpu/cpu.cfs_quota_us)
+    cpu_period=$(cat /sys/fs/cgroup/cpu/cpu.cfs_period_us)
+  fi
+  if [ -n "${cpu_quota}" ] && [ "${cpu_quota}" != 'max' ] && [ "${cpu_quota}" -gt 0 ] 2>/dev/null \
+     && [ -n "${cpu_period}" ] && [ "${cpu_period}" -gt 0 ] 2>/dev/null; then
+    # Round up, so a fractional limit still gets one worker rather than none.
+    container_cpus=$(( (cpu_quota + cpu_period - 1) / cpu_period ))
+  fi
+
+  if [ -n "${container_cpus}" ]; then
+    # A floor of 2 web workers, so a single slow request cannot block the
+    # whole container when the limit is one CPU.
+    [ -z "${WEB_WORKER_NUM}" ] && export WEB_WORKER_NUM=$(( container_cpus > 2 ? container_cpus : 2 ))
+    [ -z "${TASK_WORKER_NUM}" ] && export TASK_WORKER_NUM="${container_cpus}"
+  fi
+
   # Run with `exec` so that signals are properly handled
   exec ./bin/rr serve -c config/roadrunner/.rr.yml
 fi