start multiple types of models, with any number of instances for each

Nobody has claimed this yet.

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## 🚀 Feature

For example, I have models A, B, and C. Now, I want to start one instance of model A, two instances of model B, and two instances of model C. I have also defined the input and output classes for these models.

Is it possible to launch a service on a single port that handles one model A, two model Bs, and two model Cs, and also implements a round-robin mechanism for load balancing across the instances?"**

Let me know if you'd like a more technical version of this for a proposal, API design, or GitHub README.

### Motivation

"I am making this request because, in my work, I often use a large model (such as an LLM) along with some smaller models (like OCR). Sometimes, we prefer to have multiple instances of the OCR models, while the LLM model may only need to have one or two instances."

Start with the requirements in issue #514; no implementation files, tests, or entry points are named. Define what a single-port service supporting multiple model types and configurable instance counts should expose, including round-robin balancing, and use that behavior as the completion criterion.

Written by the indexing model from the issue text.