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 the Edit configuration button and then select the option to clone the active version. The Domains page appears.
4. Click the Settings link. The Settings page appears.

5. Click the Create cache setting button. The Create a cache setting page appears.

   

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 the Create button. The new cache setting appears on the Settings page.

8. On the Settings page, click the Attach a condition link next to the cache setting you just created. The Create a new cache condition window appears.

   

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 the Save and apply to button to create the condition.

Create new request headers

Follow these steps to create a request header within vcl_recv.

1. Click the Content link. The Content page appears.

2. Click the Create header button. The Create a header page appears.

   

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 the Create button. The new header appears on the Content page.

5. Click the Create header button to create another header to switch to the next backend. The Create a header page appears.

   

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 the Create button. 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 the Attach a condition link next to one of the headers you just created. The Create a new request condition window appears.

   

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 the Activate button to deploy your configuration changes.