Ruby

The posthog-ruby library provides tracking functionality on the server-side for applications built in Ruby.

It uses an internal queue to make calls fast and non-blocking. It also batches requests and flushes asynchronously, making it perfect to use in any part of your web app or other server-side application that needs performance.

Installation

Add this to your Gemfile:

gem "posthog-ruby"

In your app, set your API key before making any calls. If setting a custom host, make sure to include the protocol (e.g. https://).

require 'posthog'

posthog = PostHog::Client.new({
  api_key: "<ph_project_api_key>",
  host: "https://us.i.posthog.com",
  on_error: Proc.new { |status, msg| print msg }
})

You can find your project API key and instance address in the project settings page in PostHog.

Debug logging

The log level by default is set to WARN. You can change it to DEBUG if you want to debug the client by running posthog.logger.level = Logger::DEBUG, where posthog is your initialized PostHog::Client instance.

Capturing events

You can send custom events using capture:

posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: 'user_signed_up'
})

Tip: We recommend using a [object] [verb] format for your event names, where [object] is the entity that the behavior relates to, and [verb] is the behavior itself. For example, project created, user signed up, or invite sent.

Setting event properties

Optionally, you can include additional information with the event by including a properties object:

posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: 'user_signed_up',
    properties: {
        login_type: 'email',
        is_free_trial: true
    }
})

Sending pageviews

If you're aiming for a backend-only implementation of PostHog and won't be capturing events from your frontend, you can send pageviews from your backend like so:

posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: '$pageview',
    properties: {
        '$current_url': 'https://example.com'
    }
})

Person profiles and properties

The Ruby SDK captures identified events by default. These create person profiles. To set person properties in these profiles, include them when capturing an event:

posthog.capture(
    distinct_id: 'distinct_id',
    event: 'event_name',
    properties: {
        '$set': { name: 'Max Hedgehog' },
        '$set_once': { initial_url: '/blog' }
    }
)

For more details on the difference between $set and $set_once, see our person properties docs.

To capture anonymous events without person profiles, set the event's $process_person_profile property to false:

posthog.capture(
    distinct_id: 'distinct_id',
    event: 'event_name',
    properties: {
        '$process_person_profile': false
    }
)

Alias

Sometimes, you want to assign multiple distinct IDs to a single user. This is helpful when your primary distinct ID is inaccessible. For example, if a distinct ID used on the frontend is not available in your backend.

In this case, you can use alias to assign another distinct ID to the same user.

posthog.alias(
  distinct_id: "distinct_id",
  alias: "alias_id"
)

We strongly recommend reading our docs on alias to best understand how to correctly use this method.

Feature flags

PostHog's feature flags enable you to safely deploy and roll back new features as well as target specific users and groups with them.

There are 2 steps to implement feature flags in Ruby:

Step 1: Evaluate the feature flag value

Boolean feature flags

is_my_flag_enabled = posthog.is_feature_enabled('flag-key', 'distinct_id_of_your_user')

if is_my_flag_enabled
    # Do something differently for this user
    # Optional: fetch the payload
    matched_flag_payload = posthog.get_feature_flag_payload('flag-key', 'distinct_id_of_your_user')
end

Multivariate feature flags

enabled_variant = posthog.get_feature_flag('flag-key', 'distinct_id_of_your_user')

if enabled_variant == 'variant-key' # replace 'variant-key' with the key of your variant
    # Do something differently for this user
    # Optional: fetch the payload
    matched_flag_payload = posthog.get_feature_flag_payload('variant-key', 'distinct_id_of_your_user')
end

Step 2: Include feature flag information when capturing events

If you want use your feature flag to breakdown or filter events in your insights, you'll need to include feature flag information in those events. This ensures that the feature flag value is attributed correctly to the event.

Note: This step is only required for events captured using our server-side SDKs or API.

There are two methods you can use to include feature flag information in your events:

Method 1: Include the $feature/feature_flag_name property

In the event properties, include $feature/feature_flag_name: variant_key:

posthog.capture({
    distinct_id: 'distinct_id_of_your_user',
    event: 'event_name',
    properties: {
        '$feature/feature-flag-key': 'variant-key', # replace feature-flag-key with your flag key. Replace 'variant-key' with the key of your variant
    }
})

Method 2: Set send_feature_flags to true

The capture() method has an optional argument send_feature_flags, which is set to false by default. This parameter controls whether feature flag information is sent with the event.

Basic usage

Setting send_feature_flags to true will include feature flag information with the event:

posthog.capture({
    distinct_id: 'distinct_id_of_your_user',
    event: 'event_name',
    send_feature_flags: true,
})

Advanced usage (v3.1.0+)

As of version 3.1.0, send_feature_flags can also accept a hash for more granular control:

posthog.capture({
    distinct_id: 'distinct_id_of_your_user',
    event: 'event_name',
    send_feature_flags: {
        only_evaluate_locally: true,
        person_properties: { plan: 'premium' },
        group_properties: { org: { tier: 'enterprise' } }
    }
})

Performance considerations

• With local evaluation: When local evaluation is configured, setting send_feature_flags: true will not make additional server requests. Instead, it uses the locally cached feature flags, and it provides an interface for including person and/or group properties needed to evaluate the flags in the context of the event, if required.

• Without local evaluation: PostHog will make an additional request to fetch feature flag information before capturing the event, which adds delay.

Breaking change in v3.1.0

Prior to version 3.1.0, feature flags were automatically sent with events when using local evaluation, even when send_feature_flags was not explicitly set. This behavior has been removed in v3.1.0 to be more predictable and explicit.

If you were relying on this automatic behavior, you must now explicitly set send_feature_flags: true to continue sending feature flags with your events.

Fetching all flags for a user

You can fetch all flag values for a single user by calling get_all_flags() or get_all_flags_and_payloads().

This is useful when you need to fetch multiple flag values and don't want to make multiple requests.

posthog.get_all_flags('distinct_id_of_your_user')
posthog.get_all_flags_and_payloads('distinct_id_of_your_user')

Sending $feature_flag_called events

Capturing $feature_flag_called events enable PostHog to know when a flag was accessed by a user and thus provide analytics and insights on the flag. By default, we send a these event when:

1. You call posthog.get_feature_flag() or posthog.is_feature_enabled(), AND
2. It's a new user, or the value of the flag has changed.

Note: Tracking whether it's a new user or if a flag value has changed happens in a local cache. This means that if you reinitialize the PostHog client, the cache resets as well – causing $feature_flag_called events to be sent again when calling get_feature_flag or is_feature_enabled. PostHog is built to handle this, and so duplicate $feature_flag_called events won't affect your analytics.

You can disable automatically capturing $feature_flag_called events. For example, when you don't need the analytics, or it's being called at such a high volume that sending events slows things down.

To disable it, set the send_feature_flag_events argument in your function call, like so:

is_my_flag_enabled = posthog.is_feature_enabled(
    'flag-key', 
    'distinct_id_of_your_user', 
    send_feature_flag_events: true)

Advanced: Overriding server properties

Sometimes, you may want to evaluate feature flags using person properties, groups, or group properties that haven't been ingested yet, or were set incorrectly earlier.

You can provide properties to evaluate the flag with by using the person properties, groups, and group properties arguments. PostHog will then use these values to evaluate the flag, instead of any properties currently stored on your PostHog server.

For example:

posthog.get_feature_flag(
    'flag-key',
    'distinct_id_of_the_user',
    person_properties: {
        'property_name': 'value'
    },
    groups: {
        'your_group_type': 'your_group_id',
        'another_group_type': 'your_group_id',
    },
    group_properties: {
        'your_group_type': {
            'group_property_name': 'value'
        }
        'another_group_type': {
            'group_property_name': 'value'
        } 
    },
)

Overriding GeoIP properties

By default, a user's GeoIP properties are set using the IP address they use to capture events on the frontend. You may want to override the these properties when evaluating feature flags. A common reason to do this is when you're not using PostHog on your frontend, so the user has no GeoIP properties.

Currently PostHog does not provide a way to override GeoIP properties using our SDKs. Our API, however, does allow you do this. See our API docs on how to override GeoIP properties for more details.

Request timeout

You can configure the feature_flag_request_timeout_seconds parameter when initializing your PostHog client to set a flag request timeout. This helps prevent your code from being blocked in the case when PostHog's servers are too slow to respond. By default, this is set at 3 seconds.

posthog = PostHog::Client.new({
   # rest of your configuration...
   feature_flag_request_timeout_seconds: 3 # Time in seconds. Default is 3.
})

Error handling

When using the PostHog SDK, it's important to handle potential errors that may occur during feature flag operations. Here's an example of how to wrap PostHog SDK methods in an error handler:

def handle_feature_flag(client, flag_key, distinct_id)
    begin
        is_enabled = client.is_feature_enabled(flag_key, distinct_id)
        puts "Feature flag '#{flag_key}' for user '#{distinct_id}' is #{is_enabled ? 'enabled' : 'disabled'}"
        return is_enabled
    rescue => e
        puts "Error fetching feature flag '#{flag_key}': #{e.message}"
        # Optionally, you can return a default value or throw the error
        # return false # Default to disabled
        raise e
    end
end

# Usage example
try
    flag_enabled = handle_feature_flag(client, 'new-feature', 'user-123') 
    if flag_enabled
        # Implement new feature logic
    else
        # Implement old feature logic
    end
rescue => e
    # Handle the error at a higher level
    puts 'Feature flag check failed, using default behavior'
    # Implement fallback logic  
end

Local Evaluation

Evaluating feature flags requires making a request to PostHog for each flag. However, you can improve performance by evaluating flags locally. Instead of making a request for each flag, PostHog will periodically request and store feature flag definitions locally, enabling you to evaluate flags without making additional requests.

It is best practice to use local evaluation flags when possible, since this enables you to resolve flags faster and with fewer API calls.

For details on how to implement local evaluation, see our local evaluation guide.

Evaluating feature flags locally in unicorn server

If you have preload_app true in your unicorn config, you can use the after_fork hook (which is part of the unicorn's configuration) to enable the feature flag cache to receive the updates from posthog dashboard.

after_fork do |server, worker|
  $posthog = PostHog::Client.new(
    api_key: '<ph_project_api_key>',
    personal_api_key: '<ph_personal_api_key>'
    host: 'https://us.i.posthog.com',
    on_error: Proc.new { |status, msg| print msg }
  )
end

Evaluating feature flags locally in a Puma server

If you use Puma with multiple workers, you can use the on_worker_boot hook (which is part of the Puma's configuration) to enable the feature flag cache to receive the updates from PostHog.

on_worker_boot do
  $posthog = PostHog::Client.new(
    api_key: '<ph_project_api_key>',
    personal_api_key: '<ph_personal_api_key>'
    host: 'https://us.i.posthog.com',
    on_error: Proc.new { |status, msg| print msg }
  )
end

Experiments (A/B tests)

Since experiments use feature flags, the code for running an experiment is very similar to the feature flags code:

variant = posthog.get_feature_flag('experiment-feature-flag-key', 'user_distinct_id')

if variant == 'variant-name'
    # Do something
end

It's also possible to run experiments without using feature flags.

Group analytics

Group analytics allows you to associate an event with a group (e.g. teams, organizations, etc.). Read the Group Analytics guide for more information.

Note: This is a paid feature and is not available on the open-source or free cloud plan. Learn more here.

• Capture an event and associate it with a group

posthog.capture({
    distinct_id: 'distinct_id_of_the_user',
    event: 'movie_played',
    properties: {
        movie_id: '123',
        category: 'romcom'
    }
    groups: {
        'company': 'company_id_in_your_db'
    }
})

• Update properties on a group

posthog.group_identify(
  {
    group_type: "company",
    group_key: "company_id_in_your_db",
    properties: {
      name: "Awesome Inc."
    }
  }
)

The name is a special property which is used in the PostHog UI for the name of the group. If you don't specify a name property, the group ID will be used instead.

If the optional distinct_id is not provided in the group identify call, it defaults to ${groupType}_${groupKey} (e.g., $company_company_id_in_your_db in the example above). This default behavior will result in each group appearing as a separate person in PostHog. To avoid this, it's often more practical to use a consistent distinct_id, such as group_identifier.

Thank you

This library is largely based on the analytics-ruby package.