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://).

posthog = PostHog::Client.new({
  api_key: "<ph_project_api_key>",
  host: "<ph_instance_address>", # TIP: You can remove this line if you're using https://app.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 also include additional information in the event by setting the properties value:

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'
    }
})

Setting user properties

To set user properties, include the properties you'd like to set 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 user properties docs.

Alias

Sometimes, you may want to assign multiple distinct IDs to a single user. This is helpful in scenarios where your primary distinct ID may be inaccessible. For example, if a distinct ID which is typically used on the frontend is not available in certain parts of your backend code. In this case, you can use alias to assign another distinct ID to the same user.

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.

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. By setting this to true, feature flag information will automatically be sent with the event.

Note that by doing this, PostHog will make an additional request to fetch feature flag information before capturing the event. So this method is only recommended if you don't mind the extra API call and delay.

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

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')

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'
        } 
    },
)

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: '<ph_instance_address>',
    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',
    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.

Thank you

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