IIS Application Pool contains all web applications on domains hosted on your server. Dedicated IIS application pool allows your clients to have a level of isolation between web applications used by their domains. Since each dedicated application pool runs independently, errors in one application pool belonging to one client will not affect the applications running in other application pools belonging to other clients.

By default, Plesk offers a shared application pool for all your clients and their customers. However, clients and domains can use dedicated application pools if administrator and client policy permit this.

IIS application pool can work in three modes:

  • Shared pool is always used for all clients and domains.
  • Dedicated pool is always used for every client and domain.
  • Shared pool is used for clients and domains by default; clients are allowed to assign dedicated pools for their customers.

To change the IIS application pool working mode:

  1. Go to Server > IIS Application Pool.
  2. Select Global Settings tab.
  3. Select the required mode and click OK.

To limit the amount of CPU resources that the IIS application pool can use:

  1. Go to Server > IIS Application Pool.
  2. Select the Switch on CPU monitoring check box and provide a number (in percents) in the Maximum CPU use (%) field.
  3. Click OK.

To stop all applications running in the server application pool:

  1. Go to Server > IIS Application Pool.
  2. Click Stop.

To start all applications in the application pool:

  1. Go to Server > IIS Application Pool.
  2. Click Start.

To restart all applications running in the application pool:

  1. Go to Server > IIS Application Pool.
  2. Click Recycle. This can be handy if some applications are known to have memory leaks or become unstable after working for a long time.

via Configuring IIS Application Pool.