Use fixed number of Puma threads (#3773)

Instead of specifying different min and max values for the number of
threads and letting Puma start and stop threads on demand, a fixed
number of threads is configured (i.e. min = max).

Author: philippthun

lib/cloud_controller/runners/puma_runner.rb

@@ -16,7 +16,8 @@ def initialize(config, app, logger, periodic_updater, request_logs)
         end
 
         conf.workers(config.get(:puma, :workers) || 1)
-        conf.threads(0, config.get(:puma, :max_threads) || 1)
+        num_threads = config.get(:puma, :max_threads) || 1
+        conf.threads(num_threads, num_threads)
 
         # In theory there shouldn't be any open connections when shutting down Puma as they have either been gracefully
         # drained or forcefully terminated (after cc.nginx_drain_timeout) by Nginx. Puma has some built-in (i.e. not

spec/unit/lib/cloud_controller/runners/puma_runner_spec.rb

@@ -63,7 +63,7 @@ module VCAP::CloudController
         subject
 
         expect(puma_launcher.config.final_options[:workers]).to eq(num_workers)
-        expect(puma_launcher.config.final_options[:min_threads]).to eq(0)
+        expect(puma_launcher.config.final_options[:min_threads]).to eq(max_threads)
         expect(puma_launcher.config.final_options[:max_threads]).to eq(max_threads)
       end
 
@@ -75,6 +75,7 @@ module VCAP::CloudController
           subject
 
           expect(puma_launcher.config.final_options[:workers]).to eq(1)
+          expect(puma_launcher.config.final_options[:min_threads]).to eq(1)
           expect(puma_launcher.config.final_options[:max_threads]).to eq(1)
         end
       end