backend: add automatic dead instance detection

It works by having a day-long cache of
"when did we last successfully communicate with this instance?"
Anything over a specified threshold (1 month) will act as though the instance
is suspended - all outgoing jobs are dropped on processing.
The day-long cache is in place because the ordering is necessarily a
linear scan.
Once an instance comes back online, we will detect that is the case as soon as
we receive an activity from them (which will update the "last communicated at")
field.

Potential future TODOs:
* Improve the caching system, it's actually pretty inefficient as it is.
  CacheBox with a call override?
* Think of ways to make it not-a-linear-scan, since the instances table can get
  pretty big. It's around 4500 on toast cafe.

ChangeLog: Added

packages/backend/src/queue/processors/deliver.ts

@@ -12,36 +12,52 @@ import { Cache } from '@/misc/cache.js';
 import { Instance } from '@/models/entities/instance.js';
 import { StatusError } from '@/misc/fetch.js';
 import { DeliverJobData } from '@/queue/types.js';
+import { LessThan } from 'typeorm';
 
 const logger = new Logger('deliver');
 
 let latest: string | null = null;
 
 const suspendedHostsCache = new Cache<Instance[]>(1000 * 60 * 60);
+// dead host list is a linear scan, so cache it longer
+const deadHostsCache = new Cache<Instance[]>(1000 * 60 * 60 * 24);
+const deadThreshold = 1000 * 60 * 60 * 24 * 30; // 1 month
 
 export default async (job: Bull.Job<DeliverJobData>) => {
 	const { host } = new URL(job.data.to);
+	const puny = toPuny(host);
 
 	// ブロックしてたら中断
 	const meta = await fetchMeta();
-	if (meta.blockedHosts.includes(toPuny(host))) {
+	if (meta.blockedHosts.includes(puny)) {
 		return 'skip (blocked)';
 	}
 
-	// isSuspendedなら中断
+	// isSuspended
 	let suspendedHosts = suspendedHostsCache.get(null);
 	if (suspendedHosts == null) {
-		suspendedHosts = await Instances.find({
-			where: {
-				isSuspended: true,
-			},
+		suspendedHosts = await Instances.findBy({
+			isSuspended: true,
 		});
 		suspendedHostsCache.set(null, suspendedHosts);
 	}
-	if (suspendedHosts.map(x => x.host).includes(toPuny(host))) {
+	if (suspendedHosts.some(x => x.host == puny)) {
 		return 'skip (suspended)';
 	}
 
+	// dead
+	let deadHosts = deadHostsCache.get(null);
+	if (deadHosts == null) {
+		const deadTime = new Date(Date.now() - deadThreshold);
+		deadHosts = await Instances.findBy({
+			lastCommunicatedAt: LessThan(deadTime),
+		});
+		deadHostsCache.set(null, deadHosts);
+	}
+	if (deadHosts.some(x => x.host == puny)) {
+		return 'skip (dead instance)';
+	}
+
 	try {
 		if (latest !== (latest = JSON.stringify(job.data.content, null, 2))) {
 			logger.debug(`delivering ${latest}`);