Abstract: the original source www.iocoder.cn/Eureka/inst… “Taro source” welcome to reprint, keep the summary, thank you!

This article is mainly based on Eureka version 1.8.X

• 1. An overview of the
• 2. Why do you need an expiration date
• 3. EvictionTask
• Expiration logic
• 666. The eggs

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1. An overview of the

This document mainly shares the lease of eureka-server that has expired and been renewed with time.

FROM Deep Analytics Service Discovery Component Netflix Eureka

2. Why do you need an expiration date

Normally, an application instance sends an offline request to the Eureka-server. However, in actual cases, the application instance may crash abnormally or the network is abnormal, so that the offline request cannot be submitted successfully.

In this case, the Eureka-client heartbeat is used to extend the lease and the Eureka-server is used to clear the timeout lease.

3. EvictionTask

/ / AbstractInstanceRegistry Java/clean up the lease expired tasks * * * * / private final AtomicReference < EvictionTask > evictionTaskRef = new AtomicReference<EvictionTask>(); protected void postInit() { // .... If (evictionTaskRef.get()! = null) { evictionTaskRef.get().cancel(); } evictionTaskRef.set(new EvictionTask()); evictionTimer.schedule(evictionTaskRef.get(), serverConfig.getEvictionIntervalTimerInMs(), serverConfig.getEvictionIntervalTimerInMs()); }Copy the code

Expiration logic

Invoke #evict(compensationTime) to clean up the expired lease logic as follows:

1: public void evict(long additionalLeaseMs) { 2: logger.debug("Running the evict task"); 3: 4: if (! isLeaseExpirationEnabled()) { 5: logger.debug("DS: lease expiration is currently disabled."); 6: return; 7:} 8: 9: // Obtain all expired leases 10: // We collect first all expired items, to evict them in random order. For large eviction sets, 11: // if we do not that, we might wipe out whole apps before self preservation kicks in. By randomizing it, 12: // the impact should be evenly distributed across all applications. 13: List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>(); 14: for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) { 15: Map<String, Lease<InstanceInfo>> leaseMap = groupEntry.getValue(); 16: if (leaseMap ! = null) { 17: for (Entry<String, Lease<InstanceInfo>> leaseEntry : leaseMap.entrySet()) { 18: Lease<InstanceInfo> lease = leaseEntry.getValue(); 19: if (lease.isExpired(additionalLeaseMs) && lease.getHolder() ! = null) {// expired 20: expiredLeases. Add (lease); 21:} 22:} 23:} 24:} 25: 26: // Calculate the maximum number of allowable clean leases 27: // To compensate for GC pauses or drifting local time, we need to use current registry size as a base for 28: // triggering self-preservation. Without that we would wipe out full registry. 29: int registrySize = (int) getLocalRegistrySize(); 30: int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold()); 31: int evictionLimit = registrySize - registrySizeThreshold; 27: int toEvict = math.min (expiredLeases. Size (), evictionLimit); 27: int toEvict = leases. 35: if (toEvict > 0) { 36: logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit); 37: 38: // Expiration one by one 39: Random Random = new Random(System.currentTimemillis ()); 40: for (int i = 0; i < toEvict; i++) { 41: // Pick a random item (Knuth shuffle algorithm) 42: int next = i + random.nextInt(expiredLeases.size() - i); 43: Collections.swap(expiredLeases, i, next); 44: Lease<InstanceInfo> lease = expiredLeases.get(i); 45: 46: String appName = lease.getHolder().getAppName(); 47: String id = lease.getHolder().getId(); 48: EXPIRED.increment(); 49: logger.warn("DS: Registry: expired lease for {}/{}", appName, id); 50: internalCancel(appName, id, false); 51:} 52:} 53:}Copy the code

• Lines 3 to 7: The judgment allows the execution of the clearing of expired leases logic, mainly related to the self-protection mechanism, which is explained in detail in Eureka Source Code Parsing — Application Instance Registration Discovery (IV) self-protection Mechanism.

• Lines 9 through 24: Get all set of expired leases.

  • Line 19: Call the Lease#isisExpired(additionalLeaseMs) method to determine if the lease has expired as follows:

    // Lease.java
    public boolean isExpired(long additionalLeaseMs) {
       return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
    }
    
    public void renew() {
       lastUpdateTimestamp = System.currentTimeMillis() + duration;
    }
    Copy the code

    • 😈 note: Without considering the additionalLeaseMs parameter, the lease expires by one more duration than expected, LastUpdateTimestamp = system.currentTimemillis () + duration The correct setting should be lastUpdateTimestamp = System.CurrentTimemillis ().

      Note that due to renew() doing the ‘wrong” thing and setting lastUpdateTimestamp to +duration more than what it should be, the expiry will actually be 2 * duration. This is a minor bug and should only affect instances that ungracefully shutdown. Due to possible wide ranging impact to existing usage, this will not be fixed.

    • TODO [0023] : additionalLeaseMs

• Lines 26 to 34: Calculate the maximum number of leases allowed for cleanup, and then calculate the number of leases allowed for cleanup.

  • 😈 Note: Even if eureka-server turns off self-protection, if you use the default configuration renewalPercentThreshold = 0.85, the result will be batch phasing out. Here’s an example:

    // Assume 20 leases, 10 of which expire. Int registrySize = 20; Int registrySizeThreshold = (int) (20 * 0.85) = 17; int evictionLimit = 20 - 17 = 3; int toEvict = Math.min(10, 3) = 3; // After the first round of execution, 17 leases remain, of which 7 have expired. Int registrySize = 17; Int registrySizeThreshold = (int) (17 * 0.85) = 14; int evictionLimit = 17 - 14 = 3; int toEvict = Math.min(7, 3) = 3; // At the end of the second round of execution, 14 leases remain, of which 4 have expired. Int registrySize = 14; Int registrySizeThreshold = (int) (14 * 0.85) = 11; int evictionLimit = 14 - 11 = 3; int toEvict = Math.min(4, 3) = 3; // After the third round of execution, there are 11 leases left, among which 1 lease has expired. Int registrySize = 11; Int registrySizeThreshold = (int) (11 * 0.85) = 9; int evictionLimit = 11 - 9 = 2; int toEvict = Math.min(1, 2) = 1; // After the fourth round of execution, 10 leases remain, of which 0 have expired. The end.Copy the code

    • Conclusion: The difference between starting self-protection and not is whether the logic of clearing expired leases is performed. If you want to closePartial graduallyExpiration, setrenewalPercentThreshold = 0 。

  • Due to the JVM GC, or local time difference reasons, may be self protection mechanism, the threshold expectedNumberOfRenewsPerMin numberOfRenewsPerMinThreshold correctly, in relatively “dangerous” is the date of operation, Recalculate the self-protection threshold.

• Lines 35 to 51: Random clearing of expired leases. Because the lease is added to the array according to the order of applications, a random method is adopted to avoid the expiration of all applications.

  • Line 39: Pass in the current time to generate randomness for the seed, avoiding Java’s pseudo-randomness situation. In why are Random Numbers in Java pseudorandom? Have detailed analysis.
  • Lines 41 to 43: Randomly transpose the following elements to the current position (i).
• Line 50: Call#internalCancel()Method of offline expired lease inEureka Source Code Analysis — Application Instance Registration discovery (4) self-Protection MechanismHave detailed analysis.

666. The eggs

😫 originally thought a relatively easy article, turned out to consume more time than expected, maybe four hours. Mainly stuck in the compensation time, I do not understand at present. If you know fat friends, trouble to inform.

Fat friends, share my public number (impression channel source code) to your fat friends?