"SSL_read: cert already in hash table" when sending mail asynchronously

Question

I keep getting an OpenSSL::SSL::SSLError with a message of SSL_read: cert already in hash table when sending delayed e-mails out asynchronously with ActionMailer.

We use Sidekiq to send all of our e-mails out asynchronously. When posing this question as an issue in the Sidekiq GitHub repo, I was told that Sidekiq doesn't know anything about or manage the SSL connection.

Our app is hosted on Heroku, which is running OpenSSL 0.9.8k 25 Mar 2009.

We've seen this error several times in other jobs and have found that sometimes the jobs get processed, but sometimes they don't.

Is this an OpenSSL threading problem in which multiple Sidekiq threads are attempting to use the same SSL connection? Is a there a fix to this?

Here's the stacktrace we're getting:

    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/openssl/buffering.rb:175:in `sysread_nonblock`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/openssl/buffering.rb:175:in `read_nonblock`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/protocol.rb:153:in `rbuf_fill`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/protocol.rb:134:in `readuntil`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/protocol.rb:144:in `readline`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:932:in `recv_response`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:903:in `block in data`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:942:in `critical`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:896:in `data`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:663:in `block in send_message`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:852:in `rcptto_list`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:663:in `send_message`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/mail-2.5.4/lib/mail/network/delivery_methods/smtp.rb:113:in `block in deliver!`
    [PROJECT_ROOT]/vendor/ruby-2.0.0/lib/ruby/2.0.0/net/smtp.rb:521:in `start`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/mail-2.5.4/lib/mail/network/delivery_methods/smtp.rb:112:in `deliver!`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/mail-2.5.4/lib/mail/message.rb:2129:in `do_delivery`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/mail-2.5.4/lib/mail/message.rb:232:in `block in deliver`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/actionmailer-4.0.3/lib/action_mailer/base.rb:456:in `block in deliver_mail`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.3/lib/active_support/notifications.rb:159:in `block in instrument`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.3/lib/active_support/notifications/instrumenter.rb:20:in `instrument`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.3/lib/active_support/notifications.rb:159:in `instrument`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/actionmailer-4.0.3/lib/action_mailer/base.rb:454:in `deliver_mail`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/mail-2.5.4/lib/mail/message.rb:232:in `deliver`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/extensions/action_mailer.rb:20:in `perform`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/processor.rb:49:in `block (3 levels) in process`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:122:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:122:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/newrelic_rpm-3.7.1.182/lib/new_relic/agent/instrumentation/sidekiq.rb:30:in `block in call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/newrelic_rpm-3.7.1.182/lib/new_relic/agent/instrumentation/controller_instrumentation.rb:339:in `perform_action_with_newrelic_trace`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/newrelic_rpm-3.7.1.182/lib/new_relic/agent/instrumentation/sidekiq.rb:21:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:124:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-failures-0.3.0/lib/sidekiq/failures/middleware.rb:10:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:124:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-unique-jobs-2.7.0/lib/sidekiq-unique-jobs/middleware/server/unique_jobs.rb:15:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:124:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/server/active_record.rb:6:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:124:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/server/retry_jobs.rb:62:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:124:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/server/logging.rb:11:in `block in call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/logging.rb:22:in `with_context`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/server/logging.rb:7:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:124:in `block in invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:127:in `call`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/middleware/chain.rb:127:in `invoke`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/processor.rb:48:in `block (2 levels) in process`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/processor.rb:105:in `stats`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/processor.rb:47:in `block in process`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/processor.rb:86:in `do_defer`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/sidekiq-2.17.2/lib/sidekiq/processor.rb:37:in `process`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/calls.rb:25:in `public_send`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/calls.rb:25:in `dispatch`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/calls.rb:122:in `dispatch`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/actor.rb:322:in `block in handle_message`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/actor.rb:416:in `block in task`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/tasks.rb:55:in `block in initialize`
    [PROJECT_ROOT]/vendor/bundle/ruby/2.0.0/gems/celluloid-0.15.2/lib/celluloid/tasks/task_fiber.rb:13:in `block in create

Answer 1

This was related to a Ruby concurrency issue fixed in a patch for version 2.3

Your logs suggests your app is running 2.0.0. Updating the language version to at least the stable version of 2.3 would fix that problem. This can be easily done by changing your Gemfile Ruby declaration:

ruby '2.3.8'