feat: add basic healthcheck endpoint

java/app/src/main/java/org/vss/KVStore.java

@@ -11,4 +11,6 @@ public interface KVStore {
   DeleteObjectResponse delete(String userToken, DeleteObjectRequest request);
 
   ListKeyVersionsResponse listKeyVersions(String userToken, ListKeyVersionsRequest request);
+
+  void checkHealth();
 }

java/app/src/main/java/org/vss/api/HealthCheckApi.java

@@ -0,0 +1,45 @@
+package org.vss.api;
+
+import jakarta.inject.Inject;
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.core.Context;
+import jakarta.ws.rs.core.HttpHeaders;
+import jakarta.ws.rs.core.MediaType;
+import jakarta.ws.rs.core.Response;
+import lombok.extern.slf4j.Slf4j;
+import org.vss.GetObjectRequest;
+import org.vss.GetObjectResponse;
+import org.vss.KVStore;
+import org.vss.auth.AuthResponse;
+import org.vss.auth.Authorizer;
+
+@Path(VssApiEndpoint.HEALTHCHECK)
+@Slf4j
+public class HealthCheckApi {
+  KVStore kvStore;
+
+  @Inject
+  public HealthCheckApi(KVStore kvstore) {
+    this.kvStore = kvstore;
+  }
+
+  @GET
+  public Response execute(@Context HttpHeaders headers) {
+    try {
+      log.info("Healthcheck requested");
+      kvStore.checkHealth();
+      log.info("Healthcheck passed");
+
+      return Response
+        .status(Response.Status.OK)
+        .build();
+    } catch (Exception e) {
+      log.error("Exception in HealthCheckApi: ", e);
+      return Response.status(500)
+        .entity("an unexpected error occurred: " + e.getMessage())
+        .build();
+    }
+  }
+}

java/app/src/main/java/org/vss/api/VssApiEndpoint.java

@@ -1,6 +1,7 @@
 package org.vss.api;
 
 public class VssApiEndpoint {
+  public static final String HEALTHCHECK = "/health";
   public static final String GET_OBJECT = "/getObject";
   public static final String PUT_OBJECTS = "/putObjects";
   public static final String DELETE_OBJECT = "/deleteObject";

java/app/src/main/java/org/vss/impl/postgres/PostgresBackendImpl.java

@@ -47,6 +47,20 @@ public PostgresBackendImpl(DSLContext context) {
     this.context = context;
   }
 
+  @Override
+  public void checkHealth() {
+    OffsetDateTime yesterday = OffsetDateTime.now().minusDays(1);
+
+    VssDbRecord vssDbRecord = context.selectFrom(VSS_DB)
+        .where(VSS_DB.LAST_UPDATED_AT.gt(yesterday))
+        .limit(1)
+        .fetchOne();
+
+    if (vssDbRecord == null) {
+        throw new IllegalStateException("No recent records found");
+    }
+  }
+
   @Override
   public GetObjectResponse get(String userToken, GetObjectRequest request) {