Dies ist eine weitere einfache und robuste Methode, um einen Job in einem Cluster sicher auszuführen. Sie können basierend auf der Datenbank die Aufgabe nur ausführen, wenn der Knoten der "Leiter" im Cluster ist.
Auch wenn ein Knoten ausfällt oder im Cluster heruntergefahren wird, wird ein anderer Knoten zum Leader.
Alles, was Sie haben, ist, einen "Führerwahl" -Mechanismus zu erstellen und jedes Mal zu überprüfen, ob Sie der Führer sind:
@Scheduled(cron = "*/30 * * * * *")
public void executeFailedEmailTasks() {
if (checkIfLeader()) {
final List<EmailTask> list = emailTaskService.getFailedEmailTasks();
for (EmailTask emailTask : list) {
dispatchService.sendEmail(emailTask);
}
}
}
Befolgen Sie diese Schritte:
1. Definieren Sie das Objekt und die Tabelle, die einen Eintrag pro Knoten im Cluster enthalten:
@Entity(name = "SYS_NODE")
public class SystemNode {
/** The id. */
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
/** The name. */
@Column(name = "TIMESTAMP")
private String timestamp;
/** The ip. */
@Column(name = "IP")
private String ip;
/** The last ping. */
@Column(name = "LAST_PING")
private Date lastPing;
/** The last ping. */
@Column(name = "CREATED_AT")
private Date createdAt = new Date();
/** The last ping. */
@Column(name = "IS_LEADER")
private Boolean isLeader = Boolean.FALSE;
public Long getId() {
return id;
}
public void setId(final Long id) {
this.id = id;
}
public String getTimestamp() {
return timestamp;
}
public void setTimestamp(final String timestamp) {
this.timestamp = timestamp;
}
public String getIp() {
return ip;
}
public void setIp(final String ip) {
this.ip = ip;
}
public Date getLastPing() {
return lastPing;
}
public void setLastPing(final Date lastPing) {
this.lastPing = lastPing;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(final Date createdAt) {
this.createdAt = createdAt;
}
public Boolean getIsLeader() {
return isLeader;
}
public void setIsLeader(final Boolean isLeader) {
this.isLeader = isLeader;
}
@Override
public String toString() {
return "SystemNode{" +
"id=" + id +
", timestamp='" + timestamp + '\'' +
", ip='" + ip + '\'' +
", lastPing=" + lastPing +
", createdAt=" + createdAt +
", isLeader=" + isLeader +
'}';
}
}}
2.Erstellen Sie den Dienst, der a) den Knoten in die Datenbank einfügt, b) nach Leader sucht
@Service
@Transactional
public class SystemNodeServiceImpl implements SystemNodeService, ApplicationListener {
/** The logger. */
private static final Logger LOGGER = Logger.getLogger(SystemNodeService.class);
/** The constant NO_ALIVE_NODES. */
private static final String NO_ALIVE_NODES = "Not alive nodes found in list {0}";
/** The ip. */
private String ip;
/** The system service. */
private SystemService systemService;
/** The system node repository. */
private SystemNodeRepository systemNodeRepository;
@Autowired
public void setSystemService(final SystemService systemService) {
this.systemService = systemService;
}
@Autowired
public void setSystemNodeRepository(final SystemNodeRepository systemNodeRepository) {
this.systemNodeRepository = systemNodeRepository;
}
@Override
public void pingNode() {
final SystemNode node = systemNodeRepository.findByIp(ip);
if (node == null) {
createNode();
} else {
updateNode(node);
}
}
@Override
public void checkLeaderShip() {
final List<SystemNode> allList = systemNodeRepository.findAll();
final List<SystemNode> aliveList = filterAliveNodes(allList);
SystemNode leader = findLeader(allList);
if (leader != null && aliveList.contains(leader)) {
setLeaderFlag(allList, Boolean.FALSE);
leader.setIsLeader(Boolean.TRUE);
systemNodeRepository.save(allList);
} else {
final SystemNode node = findMinNode(aliveList);
setLeaderFlag(allList, Boolean.FALSE);
node.setIsLeader(Boolean.TRUE);
systemNodeRepository.save(allList);
}
}
/**
* Returns the leaded
* @param list
* the list
* @return the leader
*/
private SystemNode findLeader(final List<SystemNode> list) {
for (SystemNode systemNode : list) {
if (systemNode.getIsLeader()) {
return systemNode;
}
}
return null;
}
@Override
public boolean isLeader() {
final SystemNode node = systemNodeRepository.findByIp(ip);
return node != null && node.getIsLeader();
}
@Override
public void onApplicationEvent(final ApplicationEvent applicationEvent) {
try {
ip = InetAddress.getLocalHost().getHostAddress();
} catch (Exception e) {
throw new RuntimeException(e);
}
if (applicationEvent instanceof ContextRefreshedEvent) {
pingNode();
}
}
/**
* Creates the node
*/
private void createNode() {
final SystemNode node = new SystemNode();
node.setIp(ip);
node.setTimestamp(String.valueOf(System.currentTimeMillis()));
node.setCreatedAt(new Date());
node.setLastPing(new Date());
node.setIsLeader(CollectionUtils.isEmpty(systemNodeRepository.findAll()));
systemNodeRepository.save(node);
}
/**
* Updates the node
*/
private void updateNode(final SystemNode node) {
node.setLastPing(new Date());
systemNodeRepository.save(node);
}
/**
* Returns the alive nodes.
*
* @param list
* the list
* @return the alive nodes
*/
private List<SystemNode> filterAliveNodes(final List<SystemNode> list) {
int timeout = systemService.getSetting(SettingEnum.SYSTEM_CONFIGURATION_SYSTEM_NODE_ALIVE_TIMEOUT, Integer.class);
final List<SystemNode> finalList = new LinkedList<>();
for (SystemNode systemNode : list) {
if (!DateUtils.hasExpired(systemNode.getLastPing(), timeout)) {
finalList.add(systemNode);
}
}
if (CollectionUtils.isEmpty(finalList)) {
LOGGER.warn(MessageFormat.format(NO_ALIVE_NODES, list));
throw new RuntimeException(MessageFormat.format(NO_ALIVE_NODES, list));
}
return finalList;
}
/**
* Finds the min name node.
*
* @param list
* the list
* @return the min node
*/
private SystemNode findMinNode(final List<SystemNode> list) {
SystemNode min = list.get(0);
for (SystemNode systemNode : list) {
if (systemNode.getTimestamp().compareTo(min.getTimestamp()) < -1) {
min = systemNode;
}
}
return min;
}
/**
* Sets the leader flag.
*
* @param list
* the list
* @param value
* the value
*/
private void setLeaderFlag(final List<SystemNode> list, final Boolean value) {
for (SystemNode systemNode : list) {
systemNode.setIsLeader(value);
}
}
}}
3.Ping der Datenbank, um zu senden, dass Sie am Leben sind
@Override
@Scheduled(cron = "0 0/5 * * * ?")
public void executeSystemNodePing() {
systemNodeService.pingNode();
}
@Override
@Scheduled(cron = "0 0/10 * * * ?")
public void executeLeaderResolution() {
systemNodeService.checkLeaderShip();
}
4.Sie sind bereit! Überprüfen Sie einfach, ob Sie der Anführer sind, bevor Sie die Aufgabe ausführen:
@Override
@Scheduled(cron = "*/30 * * * * *")
public void executeFailedEmailTasks() {
if (checkIfLeader()) {
final List<EmailTask> list = emailTaskService.getFailedEmailTasks();
for (EmailTask emailTask : list) {
dispatchService.sendEmail(emailTask);
}
}
}