Where does the PAB run?

Question

I understand that PAB is a backend that:

• provides a standardized environment in which Plutus applications run
• provides disciplined state management
• presents discoverable interfaces to the external clients
• tracks on-chain information for smart contract uses
• allows developers to work in an emulated or non-emulated environment
• deals with requests such as running contract instances, forwarding user input to these instances, and notifying these instances of ledger state change events

But is it just another piece of infrastructure we should consider in our solution or is it a service we can consume for example from a third party like Blockfrost?

Answer 1

You don't have to use it in your dApp stack. As a matter of fact, many existing dApps don't use it since it's not ready. It essentially is a module/ component that makes use of existing IO products (cardano-node, cardano-db-sync or its light version of it chain-indexer etc.)

Therefore, if you want to create a dApp you can choose to use Blockfrost to keep track of your smart contract state/ fetch datum hashes/ get UTxOs etc. or you host your own instances of cardano-node/ submit-api and db-sync to do what blockfrost allows you to do and eventually PAB will as well.

PAB will offer more features than Blockfrost from what I understand.