Adjusting variable limit on concurrent code executions based on communication between frontends

A computer-implemented method to provide scaling of computational capacity on an on-demand code execution environment, the computer-implemented method comprising:

• receiving a request to execute a program code on the on-demand code execution environment, the request including client information identifying the client associated with the program code, the client associated with a set of virtual machine instance managers configured to acquire compute capacity on behalf of the client;
• requesting, based on the client information, a first virtual machine instance manager in the set of virtual machine instance managers to acquire compute capacity for executing the program code on behalf of the client;
• receiving a response indicating an inability of the first virtual machine instance manager to acquire compute capacity for executing the program code on behalf of the client;
• determining, based on load information associated with one or more frontend modules, whether a number of worker managers in the set should be adjusted, wherein the one or more frontend modules are each configured to cause code executions to be performed in response to receiving corresponding incoming code execution requests;
• in response to a determination that the number of worker managers in the set should be adjusted, causing a second virtual machine instance manager different from the first virtual machine instance manager to be added to the set;
• and
• causing at least a portion of the program code to be executed on behalf of the client on a virtual machine instance acquired by the second virtual machine instance manager.

Non-transitory physical computer storage including computer-executable instructions that, when executed by a computing system, cause the computing system to:

• receive a request to execute a program code on an on-demand code execution environment, the request including client information identifying the client associated with the program code, the client associated with a set of virtual machine instance managers configured to acquire compute capacity on behalf of the client;
• request, based on the client information, a first virtual machine instance manager in the set of virtual machine instance managers to acquire compute capacity for executing the program code on behalf of the client;
• receive a response indicating an inability of the first virtual machine instance manager to acquire compute capacity for executing the program code on behalf of the client;
• determine, based on load information associated with one or more frontend modules, whether a number of worker managers in the set should be adjusted, wherein the one or more frontend modules are each configured to cause code executions to be performed in response to receiving corresponding incoming code execution requests;
• in response to a determination that the number of worker managers in the set should be adjusted, cause a second virtual machine instance manager different from the first virtual machine instance manager to be added to the set;
• and
• cause at least a portion of the program code to be executed on behalf of the client on a virtual machine instance acquired by the second virtual machine instance manager.