  Function-as-a-Service (FaaS) struggles with burst-parallel jobs due to
needing multiple independent invocations to start a job. The lack of a group
invocation primitive complicates application development and overlooks crucial
aspects like locality and worker communication.
  We introduce a new serverless solution designed specifically for
burst-parallel jobs. Unlike FaaS, our solution ensures job-level isolation
using a group invocation primitive, allowing large groups of workers to be
launched simultaneously. This method optimizes resource allocation by
consolidating workers into fewer containers, speeding up their initialization
and enhancing locality. Enhanced locality drastically reduces remote
communication compared to FaaS, and combined with simultaneity, it enables
workers to communicate synchronously via message passing and group collectives.
This makes applications that are impractical with FaaS feasible. We implemented
our solution on OpenWhisk, providing a communication middleware that
efficiently uses locality with zero-copy messaging. Evaluations show that it
reduces job invocation and communication latency, resulting in a 2$\times$
speed-up for TeraSort and a 98.5% reduction in remote communication for
PageRank (13$\times$ speed-up) compared to traditional FaaS.
