Checking multiple backends for a single request

Using a restart is a good option to check multiple backends for a single request. This can be created using a cache setting rule and request headers.

Create a new cache setting rule

Follow these steps to create a cache restart within vcl_fetch.

1. Log in to the Fastly web interface.
2. From the Home page, select the appropriate service. You can use the search box to search by ID, name, or domain.
3. Click Edit configuration and then select the option to clone the active version.
4. Click Settings.

5. Click Create cache setting.

   

6. Fill out the Create a cache setting fields as follows:

   • In the Name field, enter Return Restart (or any meaningful, preferred name).
   • In the TTL (seconds) field, enter 0.
   • From the Action menu, select Restart processing.
   • In the Stale TTL (seconds) field, enter 0.

7. Click Create.

8. On the Settings page, click Attach a condition next to the cache setting you just created.

   

9. Fill out the Create a new cache condition fields as follows:

   • In the Name field, enter Restart Request (or any meaningful, preferred name).
   • In the Apply if field, enter beresp.status != 200 && beresp.status != 304.

10. Click Save and apply to create the condition.

Create new request headers

Follow these steps to create a request header within vcl_recv.

1. Click Content.

2. Click Create header.

   

3. Fill out the Create a new header fields as follows:

   • In the Name field, enter Fastly Internal Shielding (or any meaningful, preferred name).
   • From the Type menu, select Request, and from the Action menu, select Set.
   • In the Destination field, enter http.Fastly-Force-Shield.
   • In the Source field, enter "yes".
   • From the Ignore if set menu, select No.
   • In the Priority field, enter 10.

4. Click Create.

5. Click Create header to create another header to switch to the next backend.

   

6. Fill out the Create a header fields as follows:

   • In the Name field, enter Second Backend (or any meaningful, preferred name).
   • From the Type menu, select Request, and from the Action menu, select Set.
   • In the Destination field, enter backend.
   • In the Source field, enter Second_Backend (this should match the name of your other backend).
   • From the Ignore if set menu, select No.
   • In the Priority field, enter 11.

7. Click Create. The new header appears on the Content page.

Create new header conditions

Follow these steps to create conditions for the headers.

1. On the Content page, click Attach a condition next to one of the headers you just created.

   

2. Fill out the Create a new request condition fields as follows:

   • In the Name field, enter Req.request (or any meaningful, preferred name).
   • In the Apply if field, enter req.restarts == 1.

3. Click Save and apply to. The condition appears on the Content page.

4. Repeat steps 1-3 for the other header.

5. Click Activate to deploy your configuration changes.