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+---
+title: "Azure Foundry — Hosted Agents Model"
+author: Ruben Koster (@rkoster)
+date: 2026-07-02
+tags: [runtime-lifecycle, sandboxing-isolation, identity, observability-governance, ecosystem-survey]
+cf_areas: [diego, capi, uaa]
+status: draft
+sources:
+  - https://learn.microsoft.com/en-us/azure/foundry/agents/concepts/hosted-agents
+---
+
+## Summary
+
+Azure Foundry's hosted agents model runs agents as containerized workloads with per-session
+VM-isolated sandboxes, a persistent filesystem, and scale-to-zero with stateful resume. Each
+agent deployment gets a dedicated Microsoft Entra identity. The platform auto-injects
+OpenTelemetry traces (see `opentelemetry-genai.md`) and natively supports A2A agent
+delegation (see `a2a-protocol.md`), the Responses protocol (OpenAI-compatible), and an
+arbitrary-payload Invocations protocol.
+
+## Key findings
+
+- **Isolation model**: Per-session VM-isolated sandboxes with a persistent filesystem
+  (`$HOME` and `/files`). 15-minute idle timeout, 30-day maximum session lifetime.
+- **Packaging**: Agents are container images pushed to ACR; the platform pulls, provisions
+  compute, assigns identity, and exposes an endpoint.
+- **Identity**: Each agent deployment gets a dedicated Microsoft Entra ID created
+  automatically. Agent identity is scoped per deployment, not per session.
+- **Protocols**: Responses (OpenAI-compatible, platform-managed conversation history),
+  Invocations (arbitrary JSON, long-running async), and A2A for agent-to-agent delegation.
+- **Observability**: Built-in Application Insights; protocol libraries emit OTel traces by
+  default using the GenAI semantic conventions.
+- **Scaling**: Per-session, not per-replica — no replica count to configure; concurrent
+  sandboxes bounded by active-session quota.
+
+## CF relevance
+
+Azure Foundry illustrates what a production-grade PaaS-hosted agent model looks like when
+built from scratch with agents as first-class citizens. The container-packaging model
+parallels CF's app deployment; the per-session isolation and stateful resume go beyond CF's
+stateless process model; and the per-agent identity and auto-injected observability raise
+questions about what a platform should provide vs. what each application must wire up itself.
+
+## Open questions
+
+- Could a session-scoped state persistence model be layered onto a stateless process model,
+  or does it require a different lifecycle primitive?
+- What would an "agent buildpack" look like — protocol libraries, OTel auto-instrumentation,
+  identity bootstrap?
+- How would A2A endpoints be exposed through a platform's routing layer?
+- Is per-session VM isolation necessary, or can process-level isolation suffice for most
+  agent workloads?