tracing headers now an array (#14160)

Author: gewenyu99

contents/docs/data/sessions.mdx

@@ -32,7 +32,7 @@ A session can span multiple tabs and windows, but only on the same browser and d
 
 Activity is defined as any event sent from the client including autocapture events and replay activity like mouse movement. The inactivity period can be configured using the `session_idle_timeout_seconds` [configuration option](/docs/libraries/js/config).
 
-> **Note:** If you are [migrating data](/docs/migrate) or [using a CDP](/docs/advanced/cdp), you may need to manually set the `$session_id` property if you want to query sessions or connect them to session replays. 
+> **Note:** If you are [migrating data](/docs/migrate) or [using a CDP](/docs/advanced/cdp), you may need to manually set the `$session_id` property if you want to query sessions or connect them to session replays.
 > If you are using the JavaScript Web SDK alongside your CDP, you can get this value by calling `posthog.get_session_id()`.
 
 ## Session properties
@@ -86,9 +86,9 @@ The easiest way to analyze a session is to view a [session replay](/docs/session
 [Web analytics](/docs/web-analytics) also gives you an easily accessible overview. The top section contains sessions, session duration, and bounce rate, while further down provides more details on entry paths, exit paths, top channels, device types, and more.
 
 <ProductScreenshot
-    imageLight = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716841744/posthog.com/contents/images/docs/user-guides/sessions/web-light.png" 
+    imageLight = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716841744/posthog.com/contents/images/docs/user-guides/sessions/web-light.png"
     imageDark = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716841744/posthog.com/contents/images/docs/user-guides/sessions/web-dark.png"
-    alt="Session data in web analytics" 
+    alt="Session data in web analytics"
     classes="rounded"
 />
 
@@ -103,18 +103,18 @@ This provides the count of unique sessions where the specified event occurred. T
 To do this, select **Unique sessions** from the aggregation dropdown.
 
 <ProductScreenshot
-    imageLight = {uniqueSessionLight} 
+    imageLight = {uniqueSessionLight}
     imageDark = {uniqueSessionDark}
-    alt="Session counts" 
+    alt="Session counts"
     classes="rounded"
 />
 
 This can then be used in a formula to understand things like the average number of sessions per user or the average number of events per session.
 
 <ProductScreenshot
-    imageLight = {sessionFormulaLight} 
+    imageLight = {sessionFormulaLight}
     imageDark = {sessionFormulaDark}
-    alt="Session formula" 
+    alt="Session formula"
     classes="rounded"
 />
 
@@ -123,9 +123,9 @@ This can then be used in a formula to understand things like the average number
 You can use any of the session properties to filter your data. For example, to remove sessions that are shorter than 10 seconds, you can filter for sessions where duration is greater than 10 seconds.
 
 <ProductScreenshot
-    imageLight = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716848579/posthog.com/contents/images/docs/user-guides/sessions/duration-light.png" 
+    imageLight = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716848579/posthog.com/contents/images/docs/user-guides/sessions/duration-light.png"
     imageDark = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716848579/posthog.com/contents/images/docs/user-guides/sessions/duration-dark.png"
-    alt="Session duration filter" 
+    alt="Session duration filter"
     classes="rounded"
 />
 
@@ -134,9 +134,9 @@ You can use any of the session properties to filter your data. For example, to r
 You can plot session properties over time like you would with an event count. To do this, select one of the property aggregators (e.g. median, 90th percentile, etc.) and then select the session property to plot. For example, to plot the median session duration, select **Property value median** and then select **Session duration** as the property.
 
 <ProductScreenshot
-    imageLight = {medianDurationLight} 
+    imageLight = {medianDurationLight}
     imageDark = {medianDurationDark}
-    alt="Session median duration" 
+    alt="Session median duration"
     classes="rounded"
 />
 
@@ -149,7 +149,7 @@ This is useful for understanding entry URLs or UTMs. For example, to break down
 <ProductScreenshot
     imageLight = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716849942/posthog.com/contents/images/docs/user-guides/sessions/entry-light.png"
     imageDark = "https://res.cloudinary.com/dmukukwp6/image/upload/v1716849942/posthog.com/contents/images/docs/user-guides/sessions/entry-dark.png"
-    alt="Entry URL breakdown" 
+    alt="Entry URL breakdown"
     classes="rounded"
 />
 
@@ -163,11 +163,11 @@ If the events are logically part of the same session, e.g. a user starts a purch
 
 ### Automatically sending session IDs
 
-If you enable tracing headers within the JavaScript SDK, the session ID will be sent on every request.
+If you enable tracing headers within the JavaScript SDK, the session ID will be sent on every request. You can enable tracing headers by adding the `__add_tracing_headers` option to your `posthog.init` call:
 
 ```ts
 posthog.init('<ph_project_api_key>', {
-    __add_tracing_headers: true
+    __add_tracing_headers: ['your-backend-domain.com'] // +
 })
 ```
 

contents/docs/libraries/python/_snippets/contexts.mdx

@@ -94,7 +94,7 @@ with new_context():
 
 It's recommended to pass the currently active distinct ID from the frontend to the backend, using the `X-POSTHOG-DISTINCT-ID` header. If you're using our Django middleware, this is extracted and associated with the request handler context automatically.
 
-You can read more about identifying users in the [user identification documentation](/docs/product-analytics/identify). 
+You can read more about identifying users in the [user identification documentation](/docs/product-analytics/identify).
 
 ### Contexts and sessions
 
@@ -108,7 +108,16 @@ with new_context():
 
 <CalloutBox icon="IconInfo" title="Using PostHog on your frontend too?">
 
-If you're using the PostHog JavaScript Web SDK on your frontend, it generates a session ID for you and you can retrieve it by calling `posthog.get_session_id()`. You then need to pass that session ID to your backend by setting the `X-POSTHOG-SESSION-ID` header on each fetch request. Alternatively, you can enable '__add_tracing_headers' in your config and the header is set automatically.
+If you're using the PostHog JavaScript Web SDK on your frontend, it generates a session ID for you.
+You can pass it to your backend by adding your backend domain to `__add_tracing_headers` in your config. This will automatically add tracing headers to your requests.
+
+```js
+posthog.init('<ph_project_api_key>', {
+    __add_tracing_headers: ['your-backend-domain.com'] // +
+});
+```
+
+Alternatively, you can retrieve it on the frontend by calling `posthog.get_session_id()`. You then need to pass that session ID to your backend by setting the `X-POSTHOG-SESSION-ID` header on each fetch request.
 
 You need to extract the header in your request handler (if you're using our Django middleware integration, this happens automatically).
 

contents/docs/libraries/python/_snippets/django-context-middleware.mdx

@@ -23,8 +23,10 @@ All events captured during the request (including exceptions) will include these
 
 If you are using PostHog on your frontend, the JavaScript Web SDK will add the session and distinct ID headers automatically if you enable tracing headers.
 
-```javascript
-__add_tracing_headers: true
+```js
+posthog.init('<ph_project_api_key>', {
+    __add_tracing_headers: ['your-backend-domain.com'] // +
+})
 ```
 
 ### Exception capture

contents/tutorials/nextjs-error-monitoring.md

@@ -244,7 +244,7 @@ The context of a user and their session lives on the frontend. As such it is nec
 
 ```js
 posthog.init('<ph_project_api_key>', {
-  __add_tracing_headers: ['your-domain.com'],
+    __add_tracing_headers: ['your-backend-domain.com'] // +
 })
 ```