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ADR-0110: The idle Prolog containers are retired from every fleet, and SWI-Prolog runs only embedded in the kernel

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The record

Status: Accepted (ruling, Mohamed, 2026-10-19, verbatim: "agree to all", then "yes and document the environments thoroughly") · Date: 2026-10-19

Context

Five Incus containers exist only to hold an installed SWI-Prolog: prolog-node-1/2/3 in prod (project default, 10.53.1.16/.17/.18), prolog in test (orchestrata-test, 10.53.2.12) and prolog in dev (orchestrata-dev, 10.53.3.22). They are declared in infra/terraform/prolog.tf, test_fleet.tf and dev_fleet.tf, created by deploy/provision_environments.sh / deploy/orchestrata-test/provision_test_fleet.sh, and "probed" by swipl --version inside each one.

Measured 2026-10-19 (session audit, read-only):

• Nothing talks to them. Each runs no service beyond the base OS; ss -tnH state established inside every one returned 0 connections. No source module reads an endpoint for them: PROLOG_NODES is written only by infra/gen_env.py and read by nothing in src/; scripts/gen_level0.py falls back to "(see INFRASTRUCTURE.md)" for PROLOG_HOSTS. The env profiles carry their addresses only in comments (env/prod.env:7, env/test.env:8, env/dev.env:5). prolog.tf's own header already says the nodes "are not currently wired into app config (governance runs an in-process janus-swi engine)".
• Where Prolog actually executes. Inside the kernel process, through the vendored free-threaded janus_swi fork, loading the rules in src/orchestrata_ultimate/prolog/*.pl (29 files):
  • prod: user unit orchestrata-kernel.service on the host, /opt/orchestrata/.venv/bin/python -m orchestrata_ultimate.agents.runtime_main (/opt/orchestrata @ 0faca7a7c); /proc/<pid>/maps shows libswipl.so.9.3.8.
  • test: the same unit inside the app container (10.53.2.13, /opt/orchestrata @ 22363abb2); its maps show the same libswipl.so.9.3.8.
  • The gateway process maps no libswipl in either environment. The pytest suite and the code-intelligence tools also run Prolog in-process.
• The probe proves nothing. swipl --version in an unused container says nothing about the engine governance runs on; it gives the appearance of a "Prolog cluster" that does not exist (INFRASTRUCTURE.md, infra/README.md and claude/workflow/environments.md all list one).
• Cost. Five always-on containers (~3.7 GiB on the t9-btrfs pool plus RAM/CPU) and five addresses in the env-octet scheme.

ADR-0077 makes terraform the owner of every Incus environment, so deleting the containers by hand would be undone by the next tofu apply.

Decision (Mohamed, 2026-10-19)

1. Terraform stops declaring them. infra/terraform/prolog.tf is deleted; the prolog_nodes variable and output are removed; the "prolog" entries leave the test and dev fleet image and address maps. tofu apply destroys exactly these five instances, and the drift gate (scripts/check_infra_drift.py) is green at zero diff afterwards. The raw-machine and rehearsal templates (infra/rawmachine/, infra/rehearsal/) drop them too, so a rebuild reproduces the retired fleet, not the old one.
2. Provisioners stop creating and probing them. deploy/provision_environments.sh (role_prolog, the launch loop, the three swipl --version probes), deploy/orchestrata-test/provision_test_fleet.sh (provision_node prolog) and claude-env/install-infra.sh no longer touch Prolog containers. infra/gen_env.py no longer emits PROLOG_NODES.
3. The one place SWI-Prolog executes is in-process. The kernel (and test/tool processes) load SWI-Prolog through the janus fork. The runtime is the project-owned prefix of ADR-0095. Prolog's readiness and identity are the kernel's governance boot health line and the loaded libswipl path (ADR-0095's check), never a container probe.
4. The environment docs say so. INFRASTRUCTURE.md, infra/README.md, claude/workflow/environments.md, deploy/orchestrata-test/README.md and the env-profile comments drop the Prolog containers and state where Prolog runs.
5. An out-of-process Prolog service needs its own ADR. Nothing here forbids one. Reintroducing Prolog containers without a decision that wires and tests them is a drift finding.

Alternatives rejected

• Keep them (status quo). They cost resources, mislead every reader of the fleet docs, and the provisioning probe checks something no code depends on.
• Stop them but keep them declared. Terraform still owns them, so the drift gate either flags the stopped state or the next apply starts them; the docs stay wrong.
• incus delete by hand. Violates ADR-0077: the next tofu apply recreates all five.
• Wire them as a real remote Prolog service. No requirement asks for it. In-process janus is the load-bearing design (ADR-0095 builds the runtime for exactly that), and a network hop on every governance verdict adds latency and a new failure mode for no gain.

Consequences

• Prod (default): orchgraph-coord-1/2/3, orchgraph-data-1/2, redis-queue, prometheus-metrics. Test (orchestrata-test): app, memgraph, memgraph-ha-main, memgraph-ha-replica, redis, rh-coord-1/2/3, rh-data-1. Dev (orchestrata-dev): memgraph, redis.
• 10.53.1.16-18, 10.53.2.12 and 10.53.3.22 are free.
• Tests that named the containers change with them: tests/harness/test_incus_isolation.py, tests/scripts/test_container_cpu_accounting.py, tests/infra/test_gen_env.py and tests/infra/test_gen_env_profiles.py.
• Gates that must stay green: check_infra_drift, check_env_fleet_agreement, check_env_subnet_scheme.
• ADR-0077's rule (terraform owns every environment) stands. Only its fleet inventory changes.

Provenance

Audit run in the 2026-10-19 disk-and-fleet session (read-only measurements above). The question put to Mohamed: "Retire prolog-node-1/2/3 (prod) and prolog (test and dev) properly? That means an ADR plus changes to prolog.tf, variables.tf, the provisioning scripts and test_incus_isolation.py. Recommended, now that the kernel is confirmed as the only place Prolog runs." Mohamed, 2026-10-19, verbatim: "agree to all", then "yes and document the environments thoroughly". Related: ADR-0077 (terraform owns every environment), ADR-0095 (the SWI-Prolog runtime prefix).

Related ADRs

• Also mentioned: ADR-0077, ADR-0095

Rulings cited

None.

Specs cited

None (or no spec page exists for the ones named).