scenarios/two-nodes.yml

@@ -16,9 +16,16 @@ machines:
   anchor:
     at: { segment: hosting, address: [192.0.2.10] }
     inbound: allow
+    # The whole substrate, the registry, the builder, an adopted workload and the modules under
+    # test all land here — eleven containers before the forge arrives. At the 1GiB default this
+    # machine thrashes, and it presents as "the mesh hangs": every exec slows from 15s to 105s
+    # and the forge test fails on a status poll that is merely queued behind page-outs.
+    memory: 4GiB
+    cpus: 4
   laptop:
     at: { segment: hosting, address: [192.0.2.20] }
     inbound: allow
+    memory: 2GiB
 
 images:
   - postgres:17-alpine

src/declaration/parse.ts

@@ -37,6 +37,9 @@ function normaliseMachine(raw: unknown): Machine {
   }
   const inbound = machine["inbound"];
   if (inbound === "allow" || inbound === "deny") result.inbound = inbound;
+  if (machine["egress"] === true) result.egress = true;
+  if (machine["memory"] !== undefined) result.memory = String(machine["memory"]);
+  if (machine["cpus"] !== undefined) result.cpus = Number(machine["cpus"]);
   return result;
 }
 

src/declaration/types.ts

@@ -85,6 +85,31 @@ export interface Machine {
    * v6-addressed machine. Without this, v6 addressing would imply reachability.
    */
   inbound?: "allow" | "deny";
+  /**
+   * Whether this machine can reach the world outside the scenario.
+   *
+   * **Off unless asked for.** A scenario is a closed address space, and a machine that could
+   * reach anything would make every test's result depend on what else was reachable that day.
+   * It is declared for the same reason an address is: so what a run proves is what the scenario
+   * says, and not what the workstation happened to have.
+   *
+   * What it is for is the one thing a mesh genuinely cannot do without an outside: a first node
+   * fetching the images it starts from, before there is any mesh to serve them
+   * (novox/hq 04-ISSUES/029).
+   */
+  egress?: boolean;
+  /**
+   * How big the machine is. Absent means the lab's default, which suits a machine running a host
+   * and a handful of containers.
+   *
+   * Declared, because it is a fact about the machine the scenario describes — the node that runs
+   * the whole substrate is bigger than the laptop that joins it, and a test that starves its
+   * anchor at the default answers questions about memory pressure, not about the mesh. The forge
+   * test failed three times as "status hangs" before anyone counted the containers in 1GiB
+   * (novox/hq 04-ISSUES/024 is the same lesson about a different resource).
+   */
+  memory?: string;
+  cpus?: number;
 }
 
 /** Reachability between segments, as a segmented router enforces it. Asymmetric by design. */

src/declaration/validate.ts

@@ -204,6 +204,12 @@ export function validate(scenario: Scenario): void {
       if (machine.published?.length) {
         problems.push(`machine '${name}' is detached but declares published ports`);
       }
+      // The same fault as publishing from nowhere: raising it would drop the key on the floor,
+      // and a scenario key the runtime silently ignores is the thing this lab exists to catch.
+      if (machine.egress) {
+        problems.push(`machine '${name}' is detached but declares egress — a machine on no ` +
+          `segment reaches nothing, the world included`);
+      }
       continue;
     }
 

src/lifecycle/address.ts

@@ -23,6 +23,15 @@ export interface Wire {
   mac: string;
   addresses: string[];
   mtu: number | undefined;
+  /**
+   * Ask the host for an address rather than declaring one.
+   *
+   * **Only the uplink**, and it is the one address a scenario has no business choosing: it is on
+   * the machine's side of the host's own network, and what is routable there is the host's fact,
+   * not the declaration's. Every segment a scenario describes is still static, for the reason
+   * below.
+   */
+  dhcp?: boolean;
 }
 
 /**
@@ -31,6 +40,24 @@ export interface Wire {
  * the declaration is supposed to own.
  */
 function networkUnit(wire: Wire): string {
+  if (wire.dhcp) {
+    return [
+      "[Match]",
+      `MACAddress=${wire.mac}`,
+      "",
+      "[Network]",
+      "DHCP=ipv4",
+      "IPv6AcceptRA=no",
+      "",
+      "[DHCPv4]",
+      // **Worse than any route the scenario states.** A machine behind a declared gateway must
+      // keep using it: the uplink is a way out of the scenario, not a better way around inside
+      // it. On-link segments win regardless, being connected routes; this only settles which
+      // default route is preferred when a scenario declares one of its own.
+      "RouteMetric=4096",
+      "UseDNS=yes",
+    ].join("\n") + "\n";
+  }
   const lines = [
     "[Match]",
     `MACAddress=${wire.mac}`,
@@ -98,6 +125,16 @@ export async function applyAddresses(
       });
     }
 
+    if (spec.egress) {
+      wires.push({
+        device: `eth${spec.at.length}`,
+        mac: macFor(instanceId, machine, spec.at.length),
+        addresses: [],
+        mtu: undefined,
+        dhcp: true,
+      });
+    }
+
     for (const [index, wire] of wires.entries()) {
       const unit = networkUnit(wire);
       await incus(
@@ -109,7 +146,7 @@ export async function applyAddresses(
 
     await incus(["exec", name, "--", "systemctl", "enable", "--now", "systemd-networkd"], 60_000);
     await incus(["exec", name, "--", "systemctl", "restart", "systemd-networkd"], 60_000);
-    log(`  addressed ${machine} (${wires.map((w) => w.addresses.join(",")).join(" | ")})`);
+    log(`  addressed ${machine} (${wires.map((w) => w.dhcp ? "uplink:dhcp" : w.addresses.join(",")).join(" | ")})`);
   }
 }
 

src/lifecycle/raise.ts

@@ -131,12 +131,42 @@ async function createNetwork(
   return name;
 }
 
+/**
+ * The one network the lab supplies rather than the declaration.
+ *
+ * Every segment a scenario describes is an isolated bridge with no addresses, no DHCP and no NAT,
+ * because the declaration owns addressing. This is the opposite of that on purpose: it is not part
+ * of the scenario, it carries no scenario traffic, and what is routable on it is the host's fact.
+ *
+ * It exists so a machine can fetch what it starts from. A first node pulls three images before
+ * there is any mesh, and the module that gives a mesh its own store pulls one more
+ * (novox/hq 04-ISSUES/029) — none of which anything inside a scenario can serve.
+ *
+ * Tagged like everything else, so tearing the scenario down takes it too.
+ */
+async function createUplink(instanceId: string): Promise<string> {
+  const name = networkName(instanceId, "uplink");
+  if (await succeeds(["network", "show", name], 15_000)) return name;
+  await incus([
+    "network", "create", name,
+    "ipv4.address=auto",
+    "ipv4.nat=true",
+    "ipv6.address=none",
+    `user.mesh-lab.instance=${instanceId}`,
+    "user.mesh-lab.segment=uplink",
+  ]);
+  return name;
+}
+
 async function createMachine(
   instanceId: string,
   machine: string,
   attachments: { segment: string }[],
   image: string,
   pool: string,
+  egress = false,
+  memory = "1GiB",
+  cpus = 2,
 ): Promise<string> {
   const name = machineName(instanceId, machine);
   if (await succeeds(["config", "show", name], 15_000)) return name;
@@ -148,8 +178,8 @@ async function createMachine(
     // Arch images refuse to boot under secureboot with the shipped keys. Discovered by
     // the first launch failing with exactly that message.
     "-c", "security.secureboot=false",
-    "-c", "limits.memory=1GiB",
+    "-c", `limits.memory=${memory}`,
-    "-c", "limits.cpu=2",
+    "-c", `limits.cpu=${cpus}`,
     "-c", `user.mesh-lab.instance=${instanceId}`,
     "-c", `user.mesh-lab.machine=${machine}`,
   ];
@@ -168,6 +198,17 @@ async function createMachine(
       `hwaddr=${macFor(instanceId, machine, index)}`,
     ]);
   }
+  // After every declared attachment, so eth0..ethN keep meaning what the scenario said and the
+  // uplink is whatever comes next. A machine that never asked for one has no such interface at
+  // all, which is the difference between a closed scenario and an open one.
+  if (egress) {
+    await incus([
+      "config", "device", "add", name, `eth${attachments.length}`, "nic",
+      "nictype=bridged",
+      `parent=${await createUplink(instanceId)}`,
+      `hwaddr=${macFor(instanceId, machine, attachments.length)}`,
+    ]);
+  }
   return name;
 }
 
@@ -242,7 +283,9 @@ export async function raise(
     const byMachine = new Map<string, string>();
     for (const [machine, spec] of Object.entries(scenario.machines)) {
       const attachments = spec.at === "detached" ? [] : spec.at;
-      const name = await createMachine(instanceId, machine, attachments, image, pool);
+      const name = await createMachine(
+        instanceId, machine, attachments, image, pool,
+        spec.at !== "detached" && spec.egress === true, spec.memory, spec.cpus);
       created.push(name);
       byMachine.set(machine, name);
       log(`  machine ${machine}${spec.at === "detached" ? " (detached)" : ""}`);

test/integration/mesh.test.ts

@@ -128,8 +128,16 @@ async function settled(node: string, withinMs = 240_000): Promise<void> {
     // second is this machine's fault. The control plane is a container on the node being polled:
     // while it applies a declaration, an exec into it can lose its fifo to containerd, and a poll
     // loop that treats that as a verdict reports the mesh broken because the question missed.
-    const { out: said, ok } = await on("anchor",
+    // And a poll that *threw* — an exec timeout, a lost fifo — is also "could not ask", not a
-      `docker exec mesh-control /mesh-control status --json`);
+    // verdict. The distinction failed once as an IncusError surfacing at minute four of a wait
+    // whose machine was merely slow.
+    let said = "", ok = false;
+    try {
+      ({ out: said, ok } = await on("anchor",
+        `docker exec mesh-control /mesh-control status --json`));
+    } catch (err) {
+      said = (err as Error).message;
+    }
     if (!ok) {
       last = said;
       await new Promise((r) => setTimeout(r, 5000));

test/supported.test.ts

@@ -84,3 +84,13 @@ segments: { net: { kind: public, cidr: [192.0.2.0/24] } }
 machines: { a: { at: { segment: net, address: [192.0.2.1] }, inbound: allow } }`);
   assert.doesNotThrow(() => assertSupported(scenario));
 });
+
+test("egress is parsed, and off unless asked for", () => {
+  const scenario = parseScenario(`scenario: x
+segments: { net: { kind: public, cidr: [192.0.2.0/24] } }
+machines:
+  a: { at: { segment: net, address: [192.0.2.1] }, egress: true }
+  b: { at: { segment: net, address: [192.0.2.2] } }`);
+  assert.equal(scenario.machines["a"]?.egress, true);
+  assert.equal(scenario.machines["b"]?.egress, undefined);
+});

test/validate.test.ts

@@ -243,3 +243,10 @@ machines:
     /one gateway.*disagree.*forwardable/s,
   );
 });
+
+test("a detached machine cannot declare egress", () => {
+  refuses(`scenario: x
+segments: { net: { kind: public, cidr: [192.0.2.0/24] } }
+machines: { a: { at: detached, egress: true } }`,
+    /detached but declares egress/);
+});