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https://github.com/coinbase/temporal-ruby

Ruby SDK for Temporal
https://github.com/coinbase/temporal-ruby

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Ruby SDK for Temporal

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# Ruby SDK for Temporal



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Temporal



A pure Ruby library for defining and running Temporal workflows and activities.



To find more about Temporal itself please visit .



## Getting Started



Clone this repository:



```sh

git clone [email protected]:coinbase/temporal-ruby.git

```



Include this gem to your `Gemfile`:



```ruby

gem 'temporal-ruby', github: 'coinbase/temporal-ruby'

```



Define an activity:



```ruby

require 'temporal-ruby'

class HelloActivity < Temporal::Activity

  def execute(name)

    puts "Hello #{name}!"



    return nil

  end

end

```



Define a workflow:



```ruby

require 'path/to/hello_activity'



class HelloWorldWorkflow < Temporal::Workflow

  def execute

    HelloActivity.execute!('World')



    return nil

  end

end

```



Configure your Temporal connection and register the namespace with the Temporal service:



```ruby

require 'temporal-ruby'

Temporal.configure do |config|

  config.host = 'localhost'

  config.port = 7233

  config.namespace = 'ruby-samples'

  config.task_queue = 'hello-world'

  config.credentials = :this_channel_is_insecure

end



begin

  Temporal.register_namespace('ruby-samples', 'A safe space for playing with Temporal Ruby')

rescue Temporal::NamespaceAlreadyExistsFailure

  nil # service was already registered

end

```



Configure and start your worker process in a terminal shell:



```ruby

require 'path/to/configuration'

require 'temporal/worker'



worker = Temporal::Worker.new

worker.register_workflow(HelloWorldWorkflow)

worker.register_activity(HelloActivity)

worker.start # runs forever

```



You can add several options when initializing worker (here defaults are provided as values):



```ruby

Temporal::Worker.new(

  activity_thread_pool_size: 20, # how many threads poll for activities

  workflow_thread_pool_size: 10, # how many threads poll for workflows

  binary_checksum: nil, # identifies the version of workflow worker code

  activity_poll_retry_seconds: 0, # how many seconds to wait after unsuccessful poll for activities

  workflow_poll_retry_seconds: 0  # how many seconds to wait after unsuccessful poll for workflows

)

```



And finally start your workflow in another terminal shell:



```ruby

require 'path/to/configuration'

require 'path/to/hello_world_workflow'



Temporal.start_workflow(HelloWorldWorkflow)

```



Congratulation you've just created and executed a distributed workflow!



To view more details about your execution, point your browser to

.



There are plenty of [runnable examples](examples/) demonstrating various features of this library

available, make sure to check them out.



## Installing dependencies



Temporal service handles all the persistence, fault tolerance and coordination of your workflows and

activities. To set it up locally, download and boot the Docker Compose file from the official repo.

The Docker Compose file forwards all ports to your localhost so you can interact with

the containers easily from your shells.



Run:



```sh

curl -O https://raw.githubusercontent.com/temporalio/docker-compose/main/docker-compose.yml



docker-compose up

```



## Using Credentials



### SSL



In many production deployments you will end up connecting to your Temporal Services via SSL. In this

case you must read the public certificate of the CA that issued your Temporal server's SSL certificate and create

an instance of [gRPC Channel Credentials](https://grpc.io/docs/guides/auth/#with-server-authentication-ssltls-1).



Configure your Temporal connection:



```ruby

Temporal.configure do |config|

    config.host = 'localhost'

    config.port = 7233

    config.namespace = 'ruby-samples'

    config.task_queue = 'hello-world'

    config.credentials = GRPC::Core::ChannelCredentials.new(root_cert, client_key, client_chain)

end

```



### OAuth2 Token



Use gRPC Call Credentials to add OAuth2 token to gRPC calls:



```ruby

Temporal.configure do |config|

    config.host = 'localhost'

    config.port = 7233

    config.namespace = 'ruby-samples'

    config.task_queue = 'hello-world'

    config.credentials = GRPC::Core::CallCredentials.new(updater_proc)

end

```

`updater_proc` should be a method that returns `proc`. See an example of `updater_proc` in [googleauth](https://www.rubydoc.info/gems/googleauth/0.1.0/Signet/OAuth2/Client) library.



### Combining Credentials



To configure both SSL and OAuth2 token cedentials use `compose` method:



```ruby

Temporal.configure do |config|

    config.host = 'localhost'

    config.port = 7233

    config.namespace = 'ruby-samples'

    config.task_queue = 'hello-world'

    config.credentials = GRPC::Core::ChannelCredentials.new(root_cert, client_key, client_chain).compose(

        GRPC::Core::CallCredentials.new(token.updater_proc)

    )

end

```



## Workflows



A workflow is defined using pure Ruby code, however it should contain only a high-level

deterministic outline of the steps (their composition) that need to be executed to complete a

workflow. The actual work should be defined in your activities.



*NOTE: Keep in mind that your workflow code can get run multiple times (replayed) during the same

execution, which is why it must NOT contain any non-deterministic code (network requests, DB

queries, etc) as it can break your workflows.*



Here's an example workflow:



```ruby

class RenewSubscriptionWorkflow < Temporal::Workflow

  def execute(user_id)

    subscription = FetchUserSubscriptionActivity.execute!(user_id)

    subscription ||= CreateUserSubscriptionActivity.execute!(user_id)



    return if subscription[:active]



    ChargeCreditCardActivity.execute!(subscription[:price], subscription[:card_token])



    RenewedSubscriptionActivity.execute!(subscription[:id])

    SendSubscriptionRenewalEmailActivity.execute!(user_id, subscription[:id])

  rescue CreditCardNotChargedError => e

    CancelSubscriptionActivity.execute!(subscription[:id])

    SendSubscriptionCancellationEmailActivity.execute!(user_id, subscription[:id])

  end

end

```



In this simple workflow we are checking if a user has an active subscription and then attempt to

charge their credit card to renew an expired subscription, notifying the user of the outcome. All

the work is encapsulated in activities, while the workflow itself is responsible for calling the

activities in the right order, passing values between them and handling failures.



There is a couple of ways to execute an activity from your workflow:



```ruby

# Calls the activity by its class and blocks the execution until activity is

# finished. The return value of your activity will get assigned to the result

result = MyActivity.execute!(arg1, arg2)



# Here's a non-blocking version of the execute, returning back the future that

# will get fulfilled when activity completes. This approach allows modelling

# asynchronous workflows with activities executed in parallel

future = MyActivity.execute(arg1, arg2)

result = future.get



# Full versions of the calls from above, but has more flexibility (shown below)

result = workflow.execute_activity!(MyActivity, arg1, arg2)

future = workflow.execute_activity(MyActivity, arg1, arg2)



# In case your workflow code does not have access to activity classes (separate

# process, activities implemented in a different language, etc), you can

# simply reference them by their names

workflow.execute_activity('MyActivity', arg1, arg2, options: { namespace: 'my-namespace', task_queue: 'my-task-queue' })

```



Besides calling activities workflows can:



- Use timers

- Receive signals

- Execute other (child) workflows

- Respond to queries



## Activities



An activity is a basic unit of work that performs the desired action (potentially causing

side-effects). It can return a result or raise an error. It is defined like so:



```ruby

class CloseUserAccountActivity < Temporal::Activity

  class UserNotFound < Temporal::ActivityException; end



  def execute(user_id)

    user = User.find_by(id: user_id)



    raise UserNotFound, 'User with specified ID does not exist' unless user



    user.close_account

    user.save



    AccountClosureEmail.deliver(user)



    return nil

  end

end

```



It is important to make your activities **idempotent**, because they can get retried by Temporal (in

case a timeout is reached or your activity has thrown an error). You normally want to avoid

generating additional side effects during subsequent activity execution.



To achieve this there are two methods (returning a UUID token) available from your activity class:



- `activity.run_idem` — unique within for the current workflow execution (scoped to run_id)

- `activity.workflow_idem` — unique across all execution of the workflow (scoped to workflow_id)



Both tokens will remain the same across multiple retry attempts of the activity.



### Asynchronous completion



When dealing with asynchronous business logic in your activities, you might need to wait for an

external event to complete your activity (e.g. a callback or a webhook). This can be achieved by

manually completing your activity using a provided `async_token` from activity's context:



```ruby

class AsyncActivity < Temporal::Activity

  def execute(user_id)

    user = User.find_by(id: user_id)



    # Pass the async_token to complete your activity later

    ExternalSystem.verify_user(user, activity.async_token)



    activity.async # prevents activity from completing immediately

  end

end

```



Later when a confirmation is received you'll need to complete your activity manually using the token

provided:



```ruby

Temporal.complete_activity(async_token, result)

```



Similarly you can fail the activity by calling:



```ruby

Temporal.fail_activity(async_token, MyError.new('Something went wrong'))

```



This doesn't change the behaviour from the workflow's perspective — as any other activity the result

will be returned or an error raised.



*NOTE: Make sure to configure your timeouts accordingly and not to set heartbeat timeout (off by

default) since you won't be able to emit heartbeats and your async activities will keep timing out.*



Similar behaviour can also be achieved in other ways (one which might be more preferable in your

specific use-case), e.g.:



- by polling for a result within your activity (long-running activities with heartbeat)

- using retry policy to keep retrying activity until a result is available

- completing your activity after the initial call is made, but then waiting on a completion signal

from your workflow



## Worker



Worker is a process that communicates with the Temporal server and manages Workflow and Activity

execution. To start a worker:



```ruby

require 'temporal/worker'



worker = Temporal::Worker.new

worker.register_workflow(HelloWorldWorkflow)

worker.register_activity(SomeActivity)

worker.register_activity(SomeOtherActivity)

worker.start

```



A call to `worker.start` will take over the current process and will keep it unning until a `TERM`

or `INT` signal is received. By only registering a subset of your workflows/activities with a given

worker you can split processing across as many workers as you need.



## Starting a workflow



All communication is handled via Temporal service, so in order to start a workflow you need to send

a message to Temporal:



```ruby

Temporal.start_workflow(HelloWorldWorkflow)

```



Optionally you can pass input and other options to the workflow:



```ruby

Temporal.start_workflow(RenewSubscriptionWorkflow, user_id, options: { workflow_id: user_id })

```



Passing in a `workflow_id` allows you to prevent concurrent execution of a workflow — a subsequent

call with the same `workflow_id` will always get rejected while it is still running, raising

`Temporal::WorkflowExecutionAlreadyStartedFailure`. You can adjust the behaviour for finished

workflows by supplying the `workflow_id_reuse_policy:` argument with one of these options:



- `:allow_failed` will allow re-running workflows that have failed (terminated, cancelled, timed out or failed)

- `:allow` will allow re-running any finished workflows both failed and completed

- `:reject` will reject any subsequent attempt to run a workflow



## Execution Options



There are lots of ways in which you can configure your Workflows and Activities. The common ones

(namespace, task_queue, timeouts and retry policy) can be defined in one of these places (in the order

of precedence):



1. Inline when starting or registering a workflow/activity (use `options:` argument)

2. In your workflow/activity class definitions by calling a class method (e.g. `namespace 'my-namespace'`)

3. Globally, when configuring your Temporal library via `Temporal.configure`



## Periodic workflow execution



In certain cases you might need a workflow that runs periodically using a cron schedule. This can be

achieved using the `Temporal.schedule_workflow` API that take a periodic cron schedule as a second

argument:



```ruby

Temporal.schedule_workflow(HealthCheckWorkflow, '*/5 * * * *')

```



This will instruct Temporal to run a HealthCheckWorkflow every 5 minutes. All the rest of the

arguments are identical to the `Temporal.start_workflow` API.



*NOTE: Your execution timeout will be measured across all the workflow invocations, so make sure to

set it to allow as many invocations as you need. You can also set it to `nil`, which will use a

default value of 10 years.*



## Middleware

Middleware sits between the execution of your workflows/activities and the Temporal SDK, allowing you to insert custom code before or after the execution.



### Activity Middleware Stack

Middleware added to the activity middleware stack will be executed around each activity method. This is useful when you want to perform a certain task before and/or after each activity execution, such as logging, error handling, or measuring execution time.



### Workflow Middleware Stack

There are actually two types of workflow middleware in Temporal Ruby SDK:



*Workflow Middleware*: This middleware is executed around each entire workflow. This is similar to activity middleware, but for workflows.



*Workflow Task Middleware*: This middleware is executed around each workflow task, of which there will be many for each workflow.



### Example

To add a middleware, you need to define a class that responds to the call method. Within the call method, you should call yield to allow the next middleware in the stack (or the workflow/activity method itself if there are no more middlewares) to execute. Here's an example:



```

class MyMiddleware

  def call(metadata)

    puts "Before execution"

    yield

    puts "After execution"

    result

  end

end

```



You can add this middleware to the stack like so `worker.add_activity_middleware(MyMiddleware)`



Please note that the order of middleware in the stack matters. The middleware that is added last will be the first one to execute. In the example above, MyMiddleware will execute before any other middleware in the stack.



## Breaking Changes



Since the workflow execution has to be deterministic, breaking changes can not be simply added and

deployed — this will undermine the consistency of running workflows and might lead to unexpected

behaviour. However, breaking changes are often needed and these include:



- Adding new activities, timers, child workflows, etc.

- Remove existing activities, timers, child workflows, etc.

- Rearranging existing activities, timers, child workflows, etc.

- Adding/removing signal handlers



In order to add a breaking change you can use `workflow.has_release?(release_name)` method in your

workflows, which is guaranteed to return a consistent result whether or not it was called prior to

shipping the new release. It is also consistent for all the subsequent calls with the same

`release_name` — all of them will return the original result. Consider the following example:



```ruby

class MyWorkflow < Temporal::Workflow

  def execute

    ActivityOld1.execute!



    workflow.sleep(10)



    ActivityOld2.execute!



    return nil

  end

end

```



which got updated to:



```ruby

class MyWorkflow < Temporal::Workflow

  def execute

    Activity1.execute!



    if workflow.has_release?(:fix_1)

      ActivityNew1.execute!

    end



    workflow.sleep(10)



    if workflow.has_release?(:fix_1)

      ActivityNew2.execute!

    else

      ActivityOld.execute!

    end



    if workflow.has_release?(:fix_2)

      ActivityNew3.execute!

    end



    return nil

  end

end

```



If the release got deployed while the original workflow was waiting on a timer, `ActivityNew1` and

`ActivityNew2` won't get executed, because they are part of the same change (same release_name),

however `ActivityNew3` will get executed, since the release wasn't yet checked at the time. And for

every new execution of the workflow — all new activities will get executed, while `ActivityOld` will

not.



Later on you can clean it up and drop all the checks if you don't have any older workflows running

or expect them to ever be executed (e.g. reset).



*NOTE: Releases with different names do not depend on each other in any way.*



## Testing



It is crucial to properly test your workflows and activities before running them in production. The

provided testing framework is still limited in functionality, but will allow you to test basic

use-cases.



The testing framework is not required automatically when you require `temporal-ruby`, so you have to

do this yourself (it is strongly recommended to only include this in your test environment,

`spec_helper.rb` or similar):



```ruby

require 'temporal/testing'

```



This will allow you to execute workflows locally by running `HelloWorldWorkflow.execute_locally`.

Any arguments provided will forwarded to your `#execute` method.



In case of a higher level end-to-end integration specs, where you need to execute a Temporal workflow

as part of your code, you can enable local testing:



```ruby

Temporal::Testing.local!

```



This will treat every `Temporal.start_workflow` call as local and perform your workflows inline. It

also works with a block, restoring the original mode back after the execution:



```ruby

Temporal::Testing.local! do

  Temporal.start_workflow(HelloWorldWorkflow)

end

```



Make sure to check out [example integration specs](examples/spec/integration) for more details. Instructions

for running these integration specs can be found in [examples/README.md](examples/README.md).



## TODO



There's plenty of work to be done, but most importanly we need:



- Write specs for everything

- Implement support for missing features



## LICENSE



Copyright 2020 Coinbase, Inc.



Licensed under the Apache License, Version 2.0 (the "License");

you may not use this file except in compliance with the License.

You may obtain a copy of the License at



http://www.apache.org/licenses/LICENSE-2.0



Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.