Expose Erlang max processes and atoms in job spec

This will not work in all RabbitMQ versions, use
rabbitmq-server.additional_erl_args for greater cross-version
compatibility.

Related to rabbitmq/rabbitmq-server#1528

Author: gerhard

jobs/rabbitmq-server/spec

@@ -159,6 +159,23 @@ properties:
       The buffer limit is per distribution channel.
       A higher limit gives lower latency and higher throughput at the expense of higher memory use.
     default: 128000
+  rabbitmq-server.max_erlang_processes:
+    description: >
+      Sets the maximum number of Erlang processes.
+      Recent versions of RabbitMQ default to 1048576, which should be sufficient for most scenarios.
+      Nodes that service many clients (e.g. ~100k), or have many queues (e.g. ~50k), are known to require a higher value (e.g. 2000000).
+      A process uses 338 words when spawned (2704 bytes on 64bit architectures), including a heap of 233 words.
+      The actual maximum chosen may be much larger than the Number passed.
+      Currently the runtime system often, but not always, chooses a value that is a power of 2.
+      For more info, see http://erlang.org/doc/man/erl.html#max_processes & http://erlang.org/doc/efficiency_guide/advanced.html
+    default: 1048576
+  rabbitmq-server.max_erlang_atoms:
+    description: >
+      Sets the maximum number of Erlang atoms.
+      Recent versions of RabbitMQ default to 5000000, which should be sufficient in almost all scenarios.
+      It's unlikely that this value will need to be increased, it's exposed for consistency & transparency.
+      For more info, see http://erlang.org/doc/man/erl.html#+t & http://erlang.org/doc/efficiency_guide/advanced.html
+    default: 5000000
   rabbitmq-server.hipe_compile:
     description: >
       Set to true to precompile parts of RabbitMQ with HiPE, a just-in-time compiler for Erlang.

jobs/rabbitmq-server/templates/env.erb

@@ -39,9 +39,11 @@ export RABBITMQ_NODENAME="rabbit@<%= "#{spec.name}#{spec.index}-#{spec.deploymen
 export RABBITMQ_CLUSTER_NAME="<%= spec.deployment %>"
 
 export RABBITMQ_SCHEDULER_BIND_TYPE="<%= p("rabbitmq-server.scheduler_bind_type") %>"
+export RABBITMQ_DISTRIBUTION_BUFFER_SIZE="<%= p("rabbitmq-server.distribution_buffer_size") %>"
+export RABBITMQ_MAX_NUMBER_OF_PROCESSES="<%= p("rabbitmq-server.max_erlang_processes") %>"
+export RABBITMQ_MAX_NUMBER_OF_ATOMS="<%= p("rabbitmq-server.max_erlang_atoms") %>"
 
 export RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="<%= p("rabbitmq-server.additional_erl_args") %>"
-export RABBITMQ_DISTRIBUTION_BUFFER_SIZE="<%= p("rabbitmq-server.distribution_buffer_size") %>"
 
 export RABBITMQ_SERVER_START_ARGS="-pz /var/vcap/jobs/rabbitmq-server/packages/looking_glass/ebin -pz /var/vcap/jobs/rabbitmq-server/packages/looking_glass/deps/lz4/ebin"
 

rabbitmq-server-deployment-template.yml

@@ -67,6 +67,8 @@ instance_groups:
         hipe_compile: false
         lazy_queue_explicit_gc_run_operation_threshold: 1000
         log_levels: info
+        max_erlang_atoms: 5000000
+        max_erlang_processes: 1048576
         mirroring_flow_control: true
         mirroring_sync_batch_size: 4096
         mnesia_base: /var/vcap/store/rabbitmq-server/mnesia