Magento 2 varnish Checkout to cart Redirect Problem

Question

Preconditions

1.Magento 2.3.4

2.Must Varnish Enable

Steps to reproduce

1)Do not add any product to the cart.

2)Directly go to https://www.sample.domain/checkout/

3)Because No product in cart Redirect user to Cart page https://www.sample.domain/checkout/cart

4)Add any product in the cart.

5)Go to Checkout.

6)It will redirect you to the cart page because of the caching of step 3 in varnish.

Expected result

1)Do not add any product to the cart.

2)Directly go to https://www.sample.domain/checkout/

3)Because No product in cart Redirect user to Cart page https://www.sample.domain/checkout/cart

4)Add any product in the cart.

5)Go to Checkout.

6)It should allow the user to go to the cart when the product is available.

Actual result

Because of Varnish, It cache steps 2 and 3 redirection and next time when users come with the product at that time also it not allowing the user to go to the checkout page. So it should stop track of that redirection by varnish.

Answer 1

Checkout and cart pages should never be cached in Varnish.

Look at the default.vcl config that M2 creates. Note this line.

    # Bypass shopping cart, checkout and search requests
    if (req.url ~ "/checkout" || req.url ~ "/catalogsearch") {
        return (pass);
    }

That means that the checkout and the search should never be cached in varnish.

Did you remove that from the .vcl file for your varnish server?

Make sure you use the default vcl for the correct varnish version and modify it as you need but without removing core conditions.

There is also a cache='false' attribute that you can set on blocks in the layout that will prevent caching and I believe that they are used in the cart and checkout.

So check your theme or customization since that might be causing this issue.

---

For instance see the layout file checkout_index_index.xml in the Checkout module. That should set a block named checkout.root and that block should have the attribute cacheable set to false.

If a you have a custom module that changes this or if you made changes there make sure you did not remove that.