聊聊nacos的ServerStatusManager

@Service
public class ServerStatusManager {
​
    @Resource(name = "consistencyDelegate")
    private ConsistencyService consistencyService;
​
    @Autowired
    private SwitchDomain switchDomain;
​
    private ServerStatus serverStatus = ServerStatus.STARTING;
​
    @PostConstruct
    public void init() {
        GlobalExecutor.registerServerStatusUpdater(new ServerStatusUpdater());
    }
​
    private void refreshServerStatus() {
​
        if (StringUtils.isNotBlank(switchDomain.getOverriddenServerStatus())) {
            serverStatus = ServerStatus.valueOf(switchDomain.getOverriddenServerStatus());
            return;
        }
​
        if (consistencyService.isAvailable()) {
            serverStatus = ServerStatus.UP;
        } else {
            serverStatus = ServerStatus.DOWN;
        }
    }
​
    public ServerStatus getServerStatus() {
        return serverStatus;
    }
​
    public class ServerStatusUpdater implements Runnable {
​
        @Override
        public void run() {
            refreshServerStatus();
        }
    }
}

public enum ServerStatus {
    /**
     * server is up and ready for request
     */
    UP,
    /**
     * server is out of service, something abnormal happened
     */
    DOWN,
    /**
     * server is preparing itself for request, usually 'UP' is the next status
     */
    STARTING,
    /**
     * server is manually paused
     */
    PAUSED,
    /**
     * only write operation is permitted.
     */
    WRITE_ONLY,
    /**
     * only read operation is permitted.
     */
    READ_ONLY
}

public class TrafficReviseFilter implements Filter {
​
    @Autowired
    private ServerStatusManager serverStatusManager;
​
    @Autowired
    private SwitchDomain switchDomain;
​
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
​
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;
​
        // request limit if exist:
        String urlString = req.getRequestURI() + "?" + req.getQueryString();
        Map<String, Integer> limitedUrlMap = switchDomain.getLimitedUrlMap();
​
        if (limitedUrlMap != null && limitedUrlMap.size() > 0) {
            for (Map.Entry<String, Integer> entry : limitedUrlMap.entrySet()) {
                String limitedUrl = entry.getKey();
                if (StringUtils.startsWith(urlString, limitedUrl)) {
                    resp.setStatus(entry.getValue());
                    return;
                }
            }
        }
​
        // if server is UP:
        if (serverStatusManager.getServerStatus() == ServerStatus.UP) {
            filterChain.doFilter(req, resp);
            return;
        }
​
        // requests from peer server should be let pass:
        String agent = req.getHeader("Client-Version");
        if (StringUtils.isBlank(agent)) {
            agent = req.getHeader("User-Agent");
        }
​
        if (StringUtils.startsWith(agent, UtilsAndCommons.NACOS_SERVER_HEADER)) {
            filterChain.doFilter(req, resp);
            return;
        }
​
        // write operation should be let pass in WRITE_ONLY status:
        if (serverStatusManager.getServerStatus() == ServerStatus.WRITE_ONLY && !HttpMethod.GET.equals(req.getMethod())) {
            filterChain.doFilter(req, resp);
            return;
        }
​
        // read operation should be let pass in READ_ONLY status:
        if (serverStatusManager.getServerStatus() == ServerStatus.READ_ONLY && HttpMethod.GET.equals(req.getMethod())) {
            filterChain.doFilter(req, resp);
            return;
        }
​
        resp.getWriter().write("server is " + serverStatusManager.getServerStatus().name() + " now, please try again later!");
        resp.setStatus(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
    }
}