metacircular/PLATFORM_EVOLUTION.md

Platform Evolution

This document captures the planned evolution of the Metacircular platform from its current manually-wired state to fully declarative deployment. It is a living design document — not a spec, not a commitment, but a record of where we are, where we want to be, and what's between.

Last updated: 2026-03-28 (Phases A + B + C + D complete)

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Current State

The platform works. Services run on rift, fronted by mc-proxy, with MCIAS handling auth and Metacrypt managing secrets. MCP can deploy, stop, start, restart, and monitor containers. This is not nothing — the core infrastructure is real and operational.

But the wiring between services is manual:

• Port assignment: operators pick host ports by hand and record them in service definitions (ports = ["127.0.0.1:28443:8443"]). A mental register of "what port is free" is required.
• mc-proxy routing: routes are defined in a static TOML config file. Adding a service means editing mc-proxy-rift.toml, restarting mc-proxy, and hoping you didn't typo a port number.
• TLS certificates: provisioned manually. Certs are generated, placed in /srv/mc-proxy/certs/, and referenced by path in the mc-proxy config.
• DNS: records are manually configured in MCNS zone files.
• Container config boilerplate: operators specify network, user, restart, full image URLs, and port mappings per component, even though these are almost always the same values.
• mcdsl build wiring: the shared library requires replace directives or sibling directory tricks in Docker builds. It should be a normally-versioned Go module fetched by the toolchain.

Each new service requires touching 4-5 files across 3-4 repos. The process works but doesn't scale and is error-prone.

Target State

The operator writes a service definition that declares what they want, not how to wire it:

name = "metacrypt"
node = "rift"
version = "v1.0.0"

[build.images]
metacrypt = "Dockerfile.api"
metacrypt-web = "Dockerfile.web"

[[components]]
name = "api"

[[components.routes]]
name = "rest"
port = 8443
mode = "l4"

[[components.routes]]
name = "grpc"
port = 9443
mode = "l4"

[[components]]
name = "web"

[[components.routes]]
port = 443
mode = "l7"

Everything else is derived from conventions:

• Image name: <service> for the first/api component, <service>-<component> for others. Resolved against the registry URL from global MCP config (~/.config/mcp/mcp.toml).
• Version: the service-level version field applies to all components. Can be overridden per-component when needed.
• Volumes: /srv/<service>:/srv/<service> is the agent default. Only declare additional mounts.
• Network, user, restart: agent defaults (mcpnet, 0:0, unless-stopped). Override only when needed.
• Source path: defaults to <service> relative to the workspace root. Override with path if different.

mcp deploy metacrypt does the rest:

1. Agent assigns a free host port per route (random, check availability, retry on collision).
2. Agent requests TLS certs from Metacrypt CA for metacrypt.svc.mcp.metacircular.net.
3. Agent registers routes with mc-proxy via gRPC (mc-proxy persists them in SQLite).
4. Agent creates/updates DNS records in MCNS for metacrypt.svc.mcp.metacircular.net.
5. Agent starts containers with $PORT_REST, $PORT_GRPC, $PORT_WEB environment variables set to the assigned host ports.
6. Agent records the full state (port assignments, cert paths, route IDs) in its registry.

On teardown (mcp stop), the agent reverses the process: stops containers, removes mc-proxy routes, cleans up DNS records.

Port Environment Variables

Applications receive their assigned ports via environment variables:

Components with...	Env var	Example
Single route	$PORT	$PORT=8913
Multiple routes	$PORT_<NAME>	$PORT_REST=8913, $PORT_GRPC=9217

Route names come from the name field in [[components.routes]]. Applications read these in their config layer alongside existing env overrides (e.g., $MCR_SERVER_LISTEN_ADDR).

Hostname Convention

Every service gets <service>.svc.mcp.metacircular.net automatically. Public-facing services can additionally declare external hostnames:

[[components.routes]]
name = "web"
port = 443
mode = "l7"
hostname = "docs.metacircular.net"  # optional, public DNS

If hostname is omitted, the route uses the default <service>.svc.mcp.metacircular.net.

Multi-Node Considerations

This design targets single-node (rift) but should not prevent multi-node operation. Key design decisions that keep the door open:

• Port assignment is per-agent. Each node's agent manages its own port space. No cross-node coordination needed.
• Route registration uses the node's address, not 127.0.0.1. When mc-proxy and the service are on the same host, the backend is loopback. When they're on different hosts, the backend is the node's network address. The agent registers the appropriate address for its node. The mc-proxy route API already accepts arbitrary backend addresses.
• DNS can have multiple A records. MCNS can return multiple records for the same hostname (one per node) for simple load distribution.
• The CLI routes to the correct agent via the node field. Adding a second node is mcp node add orion <address> and then services can target node = "orion".

Nothing in the single-node implementation should hardcode assumptions about one node, one mc-proxy, or loopback-only backends.

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Gap Analysis

What exists today and works

Capability	Status
MCP CLI + agent deploy/stop/start/restart	Working
MCP sync (push service definitions to agent)	Working
MCP status/monitoring/drift detection	Working
mc-proxy L4/L7 routing	Working
mc-proxy gRPC admin API	Working
MCIAS auth for all services	Working
Metacrypt CA (PKI engine)	Working
MCNS DNS serving	Working
MCR container registry	Working
Service definitions in ~/.config/mcp/services/	Working
Image build pipeline (being folded into MCP)	Working

What needs to change

1. mcdsl: Proper Module Versioning — DONE

mcdsl is already properly versioned and released:

• Tagged releases: v0.1.0, v1.0.0, v1.0.1, v1.1.0, v1.2.0
• All consuming services import by URL with pinned versions (all consuming services on v1.2.0)
• No replace directives anywhere
• Docker builds use standard go mod download
• uses_mcdsl eliminated from service definitions and docs

2. MCP Agent: Port Assignment — DONE

Agent allocates host ports automatically at deploy time:

• Service definitions declare [[components.routes]] with name, port, mode, and optional hostname
• Agent picks random free ports (10000-60000, availability check, mutex-serialized), records assignments in component_routes table
• Containers receive $PORT / $PORT_<NAME> env vars
• Backward compatible: old-style ports strings still work unchanged
• Proto: RouteSpec message, routes + env fields on ComponentSpec
• Servicedef: RouteDef parsing and validation from TOML
• Registry: component_routes table with host_port tracking
• Runtime: Env field on ContainerSpec, -e flag generation

3. MCP Agent: mc-proxy Route Registration — DONE

Agent connects to mc-proxy via Unix socket and automatically manages routes during deploy and stop:

• Deploy: after container starts, calls AddRoute with hostname, backend (127.0.0.1:<host_port>), mode (l4/l7), and TLS cert paths
• Stop: calls RemoveRoute before stopping containers
• Config: [mcproxy] socket and cert_dir in agent config
• Nil-safe: if socket not configured, silently skipped (backward compatible)
• L7 routes: mc-proxy terminates TLS using certs at <cert_dir>/<service>.pem
• L4 routes: TLS passthrough, backend handles its own TLS
• Hostnames default to <service>.svc.mcp.metacircular.net

4. MCP Agent: TLS Cert Provisioning — DONE

Agent provisions TLS certificates from Metacrypt CA automatically during deploy for L7 routes:

• ACME client library requests certs from Metacrypt CA via its API
• Certs stored in /srv/mc-proxy/certs/<service>.pem
• Provisioning happens during deploy before mc-proxy route registration
• L7 routes get agent-provisioned certs; L4 routes use service-managed TLS

5. mc-proxy: Route Persistence — DONE

mc-proxy routes are fully persisted in SQLite and survive restarts:

• SQLite routes table stores all listener and route state
• TOML config seeds the database on first run only (via store.IsEmpty() + store.Seed()); subsequent starts load from DB (store.ListListeners() + store.ListRoutes())
• gRPC admin API (AddRoute/RemoveRoute) writes through to both DB and in-memory state
• mcproxyctl CLI provides full route management (add, remove, list)
• Routes added via gRPC survive mc-proxy restart
• TOML route config is vestigial — kept only for mc-proxy's own bootstrap before MCP is operational. The gRPC API and mcproxyctl are the primary route management interfaces going forward.

6. MCP Agent: DNS Registration — DONE

Agent automatically manages DNS records during deploy and stop:

• Deploy: calls MCNS API to create/update A records for <service>.svc.mcp.metacircular.net pointing to the node's address.
• Stop/undeploy: removes DNS records before stopping containers.
• Config: [mcns] section in agent config with server URL, CA cert, token path, zone, and node address.
• Nil-safe: if MCNS not configured, silently skipped (backward compatible).
• Authorization: mcp-agent system account can manage any record name.

7. Metacrypt: Automated Cert Issuance Policy — DONE

MCP agent has MCIAS credentials and Metacrypt policy for automated cert issuance:

• MCP agent authenticates to Metacrypt with MCIAS service credentials
• Metacrypt policy allows cert issuance for *.svc.mcp.metacircular.net
• One cert per hostname per service — no wildcard certs

8. MCNS: Record Management API — DONE

MCNS provides full CRUD for DNS records via REST and gRPC:

• REST: POST/GET/PUT/DELETE on /v1/zones/{zone}/records
• gRPC: RecordService with ListRecords, CreateRecord, GetRecord, UpdateRecord, DeleteRecord RPCs
• SQLite-backed with transactional writes, CNAME exclusivity enforcement, and automatic SOA serial bumping on mutations
• Authorization: admin can manage any record, mcp-agent system account can manage any record name, other system accounts scoped to own name
• MCP agent uses the REST API to register/deregister records on deploy/stop

9. Application $PORT Convention — DONE

mcdsl v1.2.0 added $PORT and $PORT_GRPC env var support:

• config.Load checks $PORT → overrides Server.ListenAddr
• config.Load checks $PORT_GRPC → overrides Server.GRPCAddr
• Takes precedence over TOML and generic env overrides ($MCR_SERVER_LISTEN_ADDR) — agent-assigned ports are authoritative
• Handles both config.Base embedding (MCR, MCNS, MCAT) and direct ServerConfig embedding (Metacrypt) via struct tree walking
• All consuming services on mcdsl v1.4.0

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Suggested Sequencing

The dependencies form a rough order:

Phase A — Independent groundwork: ✓ COMPLETE
  #1  mcdsl proper module versioning ✓ DONE
  #2  MCP agent port assignment ✓ DONE
  #5  mc-proxy route persistence ✓ DONE
  #9  $PORT convention in applications ✓ DONE

Phase B — MCP route registration: ✓ COMPLETE
  #3  Agent registers routes with mc-proxy ✓ DONE

Phase C — Automated TLS: ✓ COMPLETE
  #7  Metacrypt cert issuance policy ✓ DONE
  #4  Agent provisions certs ✓ DONE
      (depends on #7)

Phase D — DNS: ✓ COMPLETE
  #8  MCNS record management API ✓ DONE
  #6  Agent registers DNS ✓ DONE
      (depends on #8)

Phase E — Multi-node agent management:
  #10 Agent binary at /srv/mcp/mcp-agent on all nodes
  #11 mcp agent upgrade (SSH-based cross-compiled push)
  #12 Node provisioning tooling (Debian + NixOS)
      (depends on #10)

Phases A, B, C, and D are complete. Services can be deployed with agent-assigned ports, $PORT env vars, automatic mc-proxy route registration, automated TLS cert provisioning from Metacrypt CA, and automatic DNS registration in MCNS. No more manual port picking, mcproxyctl, TOML editing, cert generation, or DNS zone editing.

Immediate Next Steps

1. Phase E: Multi-node agent management — see below.
2. mcdoc implementation — fully designed, no platform evolution dependency. Deployable now with the new route system.

10. Agent Binary Location Convention

Gap: The agent binary is currently NixOS-managed on rift (lives in /nix/store/, systemd ExecStart points there). This doesn't work for Debian nodes and requires a full nixos-rebuild for every MCP release.

Work:

• Standardize agent binary at /srv/mcp/mcp-agent on all nodes.
• NixOS config: change ExecStart from nix store path to /srv/mcp/mcp-agent. NixOS still owns user, systemd unit, podman, directories — just not the binary version.
• Debian nodes: same layout, provisioned by setup script.

11. Agent Upgrade via SSH Push

Gap: Updating the agent requires manual, OS-specific steps. On NixOS: update flake lock, commit, push, rebuild. On Debian: build, scp, restart. With multiple nodes and architectures (amd64 + arm64), this doesn't scale.

Work:

• mcp agent upgrade [node] CLI command.
• Cross-compiles agent for each target arch (GOARCH from node config).
• Uses golang.org/x/crypto/ssh to push the binary and restart the service. No external tool dependencies.
• Node config gains ssh (hostname) and arch (GOARCH) fields.
• Upgrades all nodes by default to prevent version skew. New RPCs cause Unimplemented errors if agent and CLI are out of sync.

Depends on: #10 (binary location convention).

12. Node Provisioning Tooling

Gap: Setting up a new node requires manual steps: create user, create directories, install podman, write config, create systemd unit. Different for NixOS vs Debian.

Work:

• Go-based provisioning tool (part of MCP CLI) or standalone script.
• mcp node provision <name> SSHs to the node and runs setup: create mcp user with podman access, create /srv/mcp/, write systemd unit, install initial binary, start service.
• For NixOS, provisioning remains in the NixOS config (declarative). The provisioning tool targets Debian/generic Linux.

Depends on: #10 (binary location convention), #11 (SSH infra).

Current fleet:

Node	OS	Arch	Status
rift	NixOS	amd64	Operational, single MCP agent
hyperborea	Debian (RPi)	arm64	Online, needs agent provisioning
svc	Debian	amd64	Runs MCIAS, needs agent for public edge services

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Open Questions

• Cert rotation: when a Metacrypt-issued cert expires, does the agent renew it automatically? What's the renewal window? Does mc-proxy need to reload certs without restart?
• Public hostnames: services like mcdoc want docs.metacircular.net in addition to the .svc.mcp.metacircular.net name. Public DNS is managed outside MCNS (Cloudflare? registrar?). How does the agent handle the split between internal and external DNS?
• mc-proxy bootstrap: mc-proxy itself is a service that needs to be running before other services can be routed. Its own routes (if any) may need to be self-configured or seeded from a minimal static config at first start. Once operational, all route management goes through the gRPC API.
• Rollback: if cert provisioning fails mid-deploy, does the agent roll back the port assignment and mc-proxy route? What's the failure mode — partial deploy, full rollback, or best-effort?
• Service discovery between components: currently, components find each other via config (e.g., mcr-web knows mcr-api's gRPC address). With agent-assigned ports, components within a service need to discover each other's ports. The agent could set additional env vars ($PEER_API_GRPC=127.0.0.1:9217) or services could query the agent.