redis gem 4+ incompatibility "Specified 'redis' for Action Cable pubsub adapter, but the gem is not loaded"

[cpg]

Steps to reproduce

Using ActionCable 5.1.3 with the redis gem upgraded from 3.3.3 to 4.0.0 and attempting to broadcast on a channel seems to yield this exception:

Specified 'redis' for Action Cable pubsub adapter, but the gem is not loaded. Add `gem 'redis'` to your Gemfile (and ensure its version is at the minimum required by Action Cable).

Going back to ~> 3.3 makes AC work again as expected.

Expected behavior

AC should work

Actual behavior

An exception is raised indicating the gem is not loaded, but it seems to be.

Going back to ~> 3.3 makes AC work again as expected.

System configuration

Rails version: 5.1.3

Ruby version: 2.4.1

[KeithP]

We got this error too after bundle update. Might not be obvious to all how to diagnose from the error message - we did have gem 'redis' in our gemfile, just not the right version.

[InteNs]

same problem here, seems that AC doesn't have it's dependencies straight.

[rikkipitt]

I'm getting this today too, shall investigate further.

rails/actioncable/lib/action_cable/subscription_adapter/evented_redis.rb

Line 6 in 934327e

gem "redis", "~> 3.0"

[aldefouw]

Can confirm that this happened to me as well.

Rails Version 5.0.0.1.
Ruby Version 2.2.3

I tried running Redis 4.0 and received the error.

When I moved back to ~> 3.3 then everything was fine and web sockets worked.

[apai4]

I can also confirm that this issue persists in 5.1.4. As @rikkipitt discovered, the version constraint for the redis gem that actioncable is requesting is too strict:

rails/actioncable/lib/action_cable/subscription_adapter/evented_redis.rb

Line 4 in 813af46

gem "redis", "~> 3.0"

rails/actioncable/lib/action_cable/subscription_adapter/redis.rb

Line 3 in 813af46

gem "redis", "~> 3.0"

Which causes this exception to be raised when using a 4.x version of the redis gem (4.0.0 was released August 25):

rails/actioncable/lib/action_cable/server/configuration.rb

Line 30 in 813af46

raise Gem::LoadError, "Specified '#{adapter}' for Action Cable pubsub adapter, but the gem is not loaded. Add `gem '#{e.name}'` to your Gemfile (and ensure its version is at the minimum required by Action Cable)."

It would also be helpful for debugging if the exception being raised mentioned the specific constraint that wasn't satisfied (which should be present in the exception being caught) instead of saying the minimum required version wasn't met.

I can start a PR, but some more testing may be required before the version constraint can be relaxed since this is a major version bump @maclover7 @matthewd

[matthewd]

@jeremy is taking care of the bump in #30748, but I agree the current exception is hiding too much information. It'd be good to improve that, if anyone's up for it.

We should address the AR instance it was copied from at the same time:

rails/activerecord/lib/active_record/connection_adapters/connection_specification.rb

Line 188 in 813af46

raise Gem::LoadError, "Specified '#{spec[:adapter]}' for database adapter, but the gem is not loaded. Add `gem '#{e.name}'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord)."

[Senegal]

any updates?
I faced same issue on heroku.

versions:
ruby-2.4.0
rails: '~> 5.1.3'

but when I try to downgrade redis to 3.3.3, heroku reject my commit.

remote: Bundler Output: Warning: the running version of Bundler (1.15.2) is older than the
version that created the lockfile (1.16.0.pre.2). We suggest you upgrade to the latest version of Bundler by running gem install bundler --pre.
remote: You are trying to install in deployment mode after changing
remote: your Gemfile. Run bundle install elsewhere and add the
remote: updated Gemfile.lock to version control.
remote:
remote: The dependencies in your gemfile changed
remote:
remote: You have added to the Gemfile:
remote: * redis (= 3.3.3)
remote:
remote: You have deleted from the Gemfile:
remote: * redis (~> 3.0)
remote: !
remote: ! Failed to install gems via Bundler.
remote: !
remote: ! Push rejected, failed to compile Ruby app.

how can i fix it?

[aldefouw]

@Senegal - You probably need to run bundle install on your LOCAL development machine and then commit those updates to your repository before you try deploying again.

When you run a bundle install locally what will happen is that your Gemfile.lock file will be updated to reflect the appropriate Redis version that you are referencing in your Gemfile.

I think Heroku is rejecting because your Gemfile and Gemfile.lock have versions that do not mesh.

If you fix that and then re-deploy, you should be good to go.

[Xosmond]

Im experiencing the same problem! with Redis 4.0.1, I had to downgrade to 3.3.5

[novotarq]

I had the same problem - @Xosmond temporary(?) solution worked for me as well.

[wh1le]

Have the same problem, ruby - 2.4.0, rails - 5.0.4, had to set redis to ~> 3.2

[AnkIF]

I had the same issue.
I solved it by updating my gems (bundle update). Not sure which gem exactly solved it.
Now I have: ruby 2.5.0, rails 5.1.5, redis 4.0.1, actioncable 5.1.5.
Perhaps this method is not suitable for everyone, but it worked for me.

[Xosmond]

@AnkIF Looks like v5.1.5 was released 2 days ago.

[kimyu92]

seems like it doesn't backport to rails 5.0.7 (ruby 2.4.4) still having the same problem with redis 4
cc @eileencodes

[eileencodes]

I didn't backport 3789531 to 5-0-stable because the build wasn't failing with the error that 5-1-stable was failing with.

5.0 is only supported for security fixes now so we're likely not going to backport this to 5.0. Our recommendation is to upgrade to 5.1.

[techieroshan]

Same issue with Rails 5.0.5, Ruby 2.4

[nathan-eko]

If you can't upgrade to 5.1 because you don't have time to rewrite a ton of old Paperclip code then locking your Redis gem to 3.3.1 makes ActionCable's myopic dependency declaration happy. If you're running something else that truly demands a 4.x.x then the only practical solution seems to be vendorizing ActionCable and fixing it yourself.