whichErlangVersion.md

Which Erlang version is RabbitMQ using

We obtained the following using rabbitmqctl status|environment|report:

{running_applications,
     [{rabbitmq_web_stomp,"Rabbit WEB-STOMP - WebSockets to Stomp adapter",
          "3.6.15"},
      {rabbitmq_shovel_management,
          "Management extension for the Shovel plugin","3.6.15"},
      {rabbitmq_management,"RabbitMQ Management Console","3.6.15"},
      {rabbitmq_web_dispatch,"RabbitMQ Web Dispatcher","3.6.15"},
      {rabbitmq_stomp,"RabbitMQ STOMP plugin","3.6.15"},
      {rabbitmq_shovel,"Data Shovel for RabbitMQ","3.6.15"},
      {rabbitmq_mqtt,"RabbitMQ MQTT Adapter","3.6.15"},
      {rabbitmq_management_agent,"RabbitMQ Management Agent","3.6.15"},
      {rabbit,"RabbitMQ","3.6.15"},
      {os_mon,"CPO  CXC 138 46","2.4.2"},
      {amqp_client,"RabbitMQ AMQP Client","3.6.15"},
      {rabbit_common,
          "Modules shared by rabbitmq-server and rabbitmq-erlang-client",
          "3.6.15"},
      {compiler,"ERTS  CXC 138 10","7.0.4.1"},
      {cowboy,"Small, fast, modular HTTP server.","1.0.4"},
      {sockjs,"SockJS","0.3.4"},
      {xmerl,"XML parser","1.3.14"},
      {ranch,"Socket acceptor pool for TCP protocols.","1.3.2"},
      {recon,"Diagnostic tools for production use","2.3.2"},
      {ssl,"Erlang/OTP SSL application","8.1.3.1"},
      {public_key,"Public key infrastructure","1.4"},
      {asn1,"The Erlang ASN1 compiler version 4.0.4","4.0.4"},
      {cowlib,"Support library for manipulating Web protocols.","1.0.2"},
      {crypto,"CRYPTO","3.7.4"},
      {syntax_tools,"Syntax tools","2.1.1"},
      {inets,"INETS  CXC 138 49","6.3.9"},
      {mnesia,"MNESIA  CXC 138 12","4.14.3"},
      {sasl,"SASL  CXC 138 11","3.0.3"},
      {stdlib,"ERTS  CXC 138 10","3.3"},
      {kernel,"ERTS  CXC 138 10","5.2"}]},
{os,{unix,linux}},             
{erlang_version,
     "Erlang/OTP 19 [erts-8.3.5.3] [source] [64-bit] [smp:2:2] [async-threads:64] [hipe] [kernel-poll:true]\n"},

Given the information above, which Erlang Version is RabbitMQ running with?

We follow these steps to find that out:

1. Erlang major version

Erlang major version is 19 -> We get it from Erlang/OTP 19 [erts-8.3.5.3]

2. Erlang minor version

Erlang minor version is 3-> We get it from Erlang/OTP 19 [erts-8.3.5.3]

3. Search for the release and patch versions

We are going to search for OTP releases that bundles erts-8.3.5.3.

1. Go to https://github.com/erlang/otp/tags?after=OTP-19.3. It lists the releases older than OTP-19.3. The most recent one we get is OTP-19.2.3 . We click on Previous button so that we list the next releases.
2. On the OTP-19.3 release, we click on the ... symbol to expand it and see its content. It bundles erts-8.3 not erts-8.3.5.3.
3. We continue searching for newer OTP-19.3 versions until we find OTP-19.3.6.3 which bundles erts-8.3.5.3.
4. But to be 100% sure that is the OTP release, we need to check OTP-19.3.6.2 which happened to bundle erts-8.3.5.2. So, we are ok, OTP-19.3.6.2 is not our release.
5. However if we look at the next immediate release, which is OTP-19.3.6.4, it also bundles erts-8.3.5.3, so how do we know which OTP version are we using? We have to look for other core libraries like ssl. Our RabbitMQ is running with ssl-8.1.3.1 thus we need to find an OTP which also bundles that ssl version. We find that OTP-19.3.6.4 bundles ssl-8.1.3.1 whereas OTP-19.3.6.3 bundles ssl-8.1.3. We have finally found that RabbitMQ is running with OTP-19.3.6.4.