Add Docker healthcheck backed by Discord gateway state

Dockerfile

@@ -5,7 +5,12 @@ ARG APP_VERSION=0.0.0-SNAPSHOT
 RUN sh ./gradlew --no-daemon "-PappVersion=${APP_VERSION}" shadowJar
 
 FROM eclipse-temurin:25-jre
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends curl \
+    && rm -rf /var/lib/apt/lists/*
 WORKDIR /app
 COPY --from=builder /app/build/libs/InfinityBot-*-all.jar /app/InfinityBot.jar
 USER 10001:10001
+HEALTHCHECK --interval=30s --timeout=5s --start-period=60s --retries=3 \
+    CMD ["curl", "--fail", "--silent", "--show-error", "--noproxy", "*", "--max-time", "4", "http://127.0.0.1:8080/health"]
 ENTRYPOINT ["java", "--enable-native-access=ALL-UNNAMED", "-jar", "/app/InfinityBot.jar"]

README.md

@@ -43,6 +43,10 @@ poToken/visitor-data pairs are supplied manually and are not automatically gener
 
 Cipher support solves signature deciphering, **not** YouTube IP blocks, age restrictions, or all sign-in challenges. Test playback on the intended deployment host. See [youtube-source remote cipher documentation](https://github.com/lavalink-devs/youtube-source#using-a-remote-cipher-server).
 
+## Healthcheck
+
+The Docker image includes a healthcheck that polls JDA's Discord connection state, checking that the bot is connected rather than just running.
+
 ## Build locally
 
 Requires JDK 25. JDAVE provides Discord voice encryption (DAVE).

src/main/java/net/theinfinitymc/infinitybot/HealthCheck.java

@@ -0,0 +1,24 @@
+package net.theinfinitymc.infinitybot;
+
+import com.sun.net.httpserver.HttpServer;
+import net.dv8tion.jda.api.JDA;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+
+/** Local readiness check backed by JDA's live Discord gateway state. */
+public final class HealthCheck {
+	private HealthCheck() {}
+
+	static void start(JDA jda) throws IOException {
+		HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 8080), 0);
+		server.createContext("/health", exchange -> {
+			try {
+				exchange.sendResponseHeaders(jda.getStatus() == JDA.Status.CONNECTED ? 200 : 503, -1);
+			} finally {
+				exchange.close();
+			}
+		});
+		server.start();
+	}
+}

src/main/java/net/theinfinitymc/infinitybot/InfinityBot.java

@@ -36,6 +36,7 @@ public static void main(String[] args) {
 					.build();
 			listener.registerCommands(jda, audioManager);
 			updateActivity();
+			HealthCheck.start(jda);
 		} catch (Exception exception) {
 			throw new IllegalStateException("Failed to load InfinityBot.", exception);
 		}