How does RudderStack handle anonymousId ?

The following are the different ways in which RudderStack handles anonymousId across different SDKs:

JavaScript SDK

The RudderStack JavaScript SDK automatically generates one unique anonymousId to identify a user uniquely. It then stores it in a cookie named rl_anonymous_id and attaches it to every subsequent event. This helps in identifying the users from other sites that are hosted under a sub-domain.

Android SDK

RudderStack captures your deviceId and uses that as anonymousId for identifying the user. It is used to track the users across the application installation. To attach more information to the user, you can use the identify method.

You can use the setAnonymousId method to override and use your own anonymousId with the SDK.

iOS SDK

RudderStack captures deviceId and uses that as anonymousId for identifying the user. To attach more information to the user, you can use the identify method.

You can use the setAnonymousId method to override and use your own anonymousId with the SDK.

How do I identify anonymous users across client-side and server-side?

To identify anonymous users across both client-side and server-side, it is advisable to use a separate, new cookie at your end.

During the user's first visit, your server generates a new anonymousId to make the event calls using the server-side SDKs and sends the set_cookie response to the browser to set the visitor_id cookie.

• If the RudderStack JavaScript SDK is not blocked, you can use the setAnonymousId method to set the same value as the visitor_id.
• In case the RudderStack JavaScript SDK is blocked, still the next requests to the server will have the visitor_id cookie which can be used by the server-side events for anonymousId.

To set anonymousId, use the setAnonymousId call after the SDK snippet as below:

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rudderanalytics.setAnonymousId("my-anon-id");

To get the anonymousId stored in a RudderStack cookie, use the getAnonymousId call inside the ready callback - this ensures that the method is available and returns the previously set anonymousId value.

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rudderanalytics.ready(
    () => {
      var anonId = window.rudderanalytics.getAnonymousId();
        console.log(anonId);
    }
);

What is RudderStack's retry and backoff logic after the connection fails?

When the dataplane gets disconnected from the SDK and events are no longer able to be sent to Rudder Server, then some of the SDK's will store events and retry sending them to Rudder Server with a certain backoff logic.

General support and logic

JavaScript SDK

This SDK can be configured to match your requirements for retry and backoff logic. By default, if the dataplane goes down and the JS SDK cannot send events to the Rudder Server, up to 100 events will be stored. While still disconnected from the dataplane, the JS SDK will try to resend the stored events to the Rudder Server. However, for each retry, the delay duration will grow. The equation to get the duration of delay is as follows:

Where, $dt$ is the delay time in ms, $md$ is the minRetryDelay (configurable; default is 1000 ms), $F$ is the backoffFactor (configurable; default is 2), and $n$ is the current retry attempt. The SDK will retry until the attempts surpass the maxAttempts value. This is by default set to 10 attempts but is configurable. Each retry attempt, the delay time grows exponentially. However, it will max out at whatever the maxRetryDelay is. By default, this value is set at 360000 ms, but it is configurable.

iOS and Android SDK

Both the iOS and Android SDKs share similar retry and backoff logic for when the dataplane connection fails. If the dataplane goes down, up to 10,000 events will be stored. There is no limit to how many times the SDK will try to send failed events. However, the delay duration in between the attempts will grow by 1 second after each retry. For example, after the first failed attempt, there will be a delay of 1 second. After the second failed attempt, the SDK will wait 2 seconds before it retries. The third failed attempt will cause a delay of 3 seconds, and this behavior will repeat until the connection is re-established.

Node SDK

Currently the Node SDK is the only server-side SDK that supports event retry and backoff logic. The logic is quite similar to the JavaScript SDK. If the connection fails, up to 20,000 events will be stored. However, this is in-memory storage and can result in data loss. The SDK will retry a maximum of 10 times, by default. For each retry the delay duration between retries will grow and can be calculated using the following equation.

Where, $dt$ is the delay time in ms and $n$ is the current retry attempt. The SDK will retry until the attempts surpass the maxAttempts value which is set to 10 attempts. With each retry attempt, the delay time will grow exponentially. However, it will never be greater than the maximum delay duration which is 30 seconds.

Can I filter and selectively send the event data to certain destinations?

Yes, you can use RudderStack's Client-side Event Filtering feature to specify which events should be discarded or allowed to flow through - by allowlisting or denylisting them in the RudderStack dashboard while setting up your destination. This method is useful if you are sending the events via the device mode.