eureka集群基於DNS配置方式

本文轉載自查看原文 2017-06-28 16:30 5065 use-dns-for-fetching-service-urls/ useDnsForFetchingServiceUrls/ eureka/ dns/ ha/ eurekaServerDNSName

最近在研究spring cloud eureka集群配置的時候碰到問題:多台eureka server如果需要互相注冊,需要在配置文件中將其他服務器地址配置寫死.同樣客戶端啟用服務發現功能(eureka client)也需要配置服務端地址列表(其實eureka server與其他eureka server通信也是用的是eureka client組件).按照官方案例提供3台server,如果現在需要增加第四台,第五台...那么問題就來了,所有eureka client的serverUrls列表是否都得更新(修改配置文件)?

一句話總結如上問題就是:eureka集群有什么辦法能支持動態集群(集群數量可增減客戶端不需要改動任何內容)?

經過尋找發現spring cloud eureka client提供一個eureka.client.useDnsForFetchingServiceUrls選項,使用Dns獲取服務地址.

經過各種了解,明確了該配置項就是啟用dns來存儲eureka server列表的,可以實現動態eureka server集群的功能.但是問題又來了,相關屬性還有那些?dns又該如何配置呢?

相關屬性好找,有網友提供的例子,dns這塊沒有比較明確的說明,為了弄明白這塊自己嘗試着看了看源碼,結果找到了DNS里面關於具體如何使用DNS結果的相關代碼.代碼如下:

getDiscoveryServiceUrls的作用是獲取所有eureka service urls,該方法首先判斷是否需要從DNS獲取服務列表,圖中紅框部分就是從DNS獲取服務列表,繼續往下分析:

在分析之前,插播一個知識點:eureka集群與region和zone這幾個概念的關系.http://www.vccoo.com/v/bqq4vj

繼續看代碼:

 1 /**
 2      * Get the list of all eureka service urls from DNS for the eureka client to
 3      * talk to. The client picks up the service url from its zone and then fails over to
 4      * other zones randomly. If there are multiple servers in the same zone, the client once
 5      * again picks one randomly. This way the traffic will be distributed in the case of failures.
 6      *
 7      * @param clientConfig the clientConfig to use
 8      * @param instanceZone The zone in which the client resides.
 9      * @param preferSameZone true if we have to prefer the same zone as the client, false otherwise.
10      * @param randomizer a randomizer to randomized returned urls
11      *
12      * @return The list of all eureka service urls for the eureka client to talk to.
13      */
14     public static List<String> getServiceUrlsFromDNS(EurekaClientConfig clientConfig, String instanceZone, boolean preferSameZone, ServiceUrlRandomizer randomizer) {
15         String region = getRegion(clientConfig);
16         // Get zone-specific DNS names for the given region so that we can get a
17         // list of available zones
18         Map<String, List<String>> zoneDnsNamesMap = getZoneBasedDiscoveryUrlsFromRegion(clientConfig, region);
19         Set<String> availableZones = zoneDnsNamesMap.keySet();
20         List<String> zones = new ArrayList<String>(availableZones);
21         if (zones.isEmpty()) {
22             throw new RuntimeException("No available zones configured for the instanceZone " + instanceZone);
23         }
24         int zoneIndex = 0;
25         boolean zoneFound = false;
26         for (String zone : zones) {
27             logger.debug("Checking if the instance zone {} is the same as the zone from DNS {}", instanceZone, zone);
28             if (preferSameZone) {
29                 if (instanceZone.equalsIgnoreCase(zone)) {
30                     zoneFound = true;
31                 }
32             } else {
33                 if (!instanceZone.equalsIgnoreCase(zone)) {
34                     zoneFound = true;
35                 }
36             }
37             if (zoneFound) {
38                 Object[] args = {zones, instanceZone, zoneIndex};
39                 logger.debug("The zone index from the list {} that matches the instance zone {} is {}", args);
40                 break;
41             }
42             zoneIndex++;
43         }
44         if (zoneIndex >= zones.size()) {
45             logger.warn("No match for the zone {} in the list of available zones {}",
46                     instanceZone, Arrays.toString(zones.toArray()));
47         } else {
48             // Rearrange the zones with the instance zone first
49             for (int i = 0; i < zoneIndex; i++) {
50                 String zone = zones.remove(0);
51                 zones.add(zone);
52             }
53         }
54 
55         // Now get the eureka urls for all the zones in the order and return it
56         List<String> serviceUrls = new ArrayList<String>();
57         for (String zone : zones) {
58             for (String zoneCname : zoneDnsNamesMap.get(zone)) {
59                 List<String> ec2Urls = new ArrayList<String>(getEC2DiscoveryUrlsFromZone(zoneCname, DiscoveryUrlType.CNAME));
60                 // Rearrange the list to distribute the load in case of
61                 // multiple servers
62                 if (ec2Urls.size() > 1) {
63                     randomizer.randomize(ec2Urls);
64                 }
65                 for (String ec2Url : ec2Urls) {
66                     String serviceUrl = "http://" + ec2Url + ":"
67                             + clientConfig.getEurekaServerPort()
68                             + "/" + clientConfig.getEurekaServerURLContext()
69                             + "/";
70                     logger.debug("The EC2 url is {}", serviceUrl);
71                     serviceUrls.add(serviceUrl);
72                 }
73             }
74         }
75         // Rearrange the fail over server list to distribute the load
76         String primaryServiceUrl = serviceUrls.remove(0);
77         randomizer.randomize(serviceUrls);
78         serviceUrls.add(0, primaryServiceUrl);
79 
80         logger.debug("This client will talk to the following serviceUrls in order : {} ",
81                 Arrays.toString(serviceUrls.toArray()));
82         return serviceUrls;
83     }

從代碼中可以看到,首先獲取當前eureka-client所在的region,然后根據region獲取所有zone以及對應的域名信息,然后循環所有zone域名信息獲取eureka-server地址,拼接成完整的serviceUrl並加入serviceUrls列表中.

拼接的serviceUrl格式為:"http://" + ec2Url + ":" + clientConfig.getEurekaServerPort() + "/" + clientConfig.getEurekaServerURLContext() + "/";

另外在代碼中有標出兩處重點,紅色背景的是根據region獲取zone的具體方法,藍色背景的是根據zone具體地址獲取eureka地址列表的方法.重點就在這兩個方法中.

首先看第一個,獲取zone的邏輯:

 1     /**
 2      * Get the zone based CNAMES that are bound to a region.
 3      *
 4      * @param region
 5      *            - The region for which the zone names need to be retrieved
 6      * @return - The list of CNAMES from which the zone-related information can
 7      *         be retrieved
 8      */
 9     public static Map<String, List<String>> getZoneBasedDiscoveryUrlsFromRegion(EurekaClientConfig clientConfig, String region) {
10         String discoveryDnsName = null;
11         try {
12             discoveryDnsName = "txt." + region + "." + clientConfig.getEurekaServerDNSName();
13 
14             logger.debug("The region url to be looked up is {} :", discoveryDnsName);
15             Set<String> zoneCnamesForRegion = new TreeSet<String>(DnsResolver.getCNamesFromTxtRecord(discoveryDnsName));
16             Map<String, List<String>> zoneCnameMapForRegion = new TreeMap<String, List<String>>();
17             for (String zoneCname : zoneCnamesForRegion) {
18                 String zone = null;
19                 if (isEC2Url(zoneCname)) {
20                     throw new RuntimeException(
21                             "Cannot find the right DNS entry for "
22                                     + discoveryDnsName
23                                     + ". "
24                                     + "Expected mapping of the format <aws_zone>.<domain_name>");
25                 } else {
26                     String[] cnameTokens = zoneCname.split("\\.");
27                     zone = cnameTokens[0];
28                     logger.debug("The zoneName mapped to region {} is {}", region, zone);
29                 }
30                 List<String> zoneCnamesSet = zoneCnameMapForRegion.get(zone);
31                 if (zoneCnamesSet == null) {
32                     zoneCnamesSet = new ArrayList<String>();
33                     zoneCnameMapForRegion.put(zone, zoneCnamesSet);
34                 }
35                 zoneCnamesSet.add(zoneCname);
36             }
37             return zoneCnameMapForRegion;
38         } catch (Throwable e) {
39             throw new RuntimeException("Cannot get cnames bound to the region:" + discoveryDnsName, e);
40         }
41     }

12行是請求dns中的地址格式:"txt." + region + "." + clientConfig.getEurekaServerDNSName(),例如:txt.region1.baidu.com,txt.region1.163.com,txt.region2.163.com等

17,27,35行是對返回結果的解析邏輯,可以看出返回值應當是多條記錄並且以空格分開(在15行方法內),每條記錄都應當是一個域名並且第一個.之前的部分作為zone名稱,最終按照zone組織成zone:List<區域地址>的結果返回.

再看第二個,獲取eureka server地址邏輯:

 1     /**
 2      * Get the list of EC2 URLs given the zone name.
 3      *
 4      * @param dnsName The dns name of the zone-specific CNAME
 5      * @param type CNAME or EIP that needs to be retrieved
 6      * @return The list of EC2 URLs associated with the dns name
 7      */
 8     public static Set<String> getEC2DiscoveryUrlsFromZone(String dnsName, DiscoveryUrlType type) {
 9         Set<String> eipsForZone = null;
10         try {
11             dnsName = "txt." + dnsName;
12             logger.debug("The zone url to be looked up is {} :", dnsName);
13             Set<String> ec2UrlsForZone = DnsResolver.getCNamesFromTxtRecord(dnsName);
14             for (String ec2Url : ec2UrlsForZone) {
15                 logger.debug("The eureka url for the dns name {} is {}", dnsName, ec2Url);
16                 ec2UrlsForZone.add(ec2Url);
17             }
18             if (DiscoveryUrlType.CNAME.equals(type)) {
19                 return ec2UrlsForZone;
20             }
21             eipsForZone = new TreeSet<String>();
22             for (String cname : ec2UrlsForZone) {
23                 String[] tokens = cname.split("\\.");
24                 String ec2HostName = tokens[0];
25                 String[] ips = ec2HostName.split("-");
26                 StringBuilder eipBuffer = new StringBuilder();
27                 for (int ipCtr = 1; ipCtr < 5; ipCtr++) {
28                     eipBuffer.append(ips[ipCtr]);
29                     if (ipCtr < 4) {
30                         eipBuffer.append(".");
31                     }
32                 }
33                 eipsForZone.add(eipBuffer.toString());
34             }
35             logger.debug("The EIPS for {} is {} :", dnsName, eipsForZone);
36         } catch (Throwable e) {
37             throw new RuntimeException("Cannot get cnames bound to the region:" + dnsName, e);
38         }
39         return eipsForZone;
40     }

11行代碼明確了請求格式為:"txt." + dnsName,例如:txt.zone1.163.com,txt.zone2.baidu.com等

而返回結果則比較復雜,我們只關心cnametype的,從getServiceUrlsFromDNS方法中可以得知,只需要返回服務器地址或域名就可以了(返回多組同樣用空格隔開).

看到這里對dns獲取eureka地址的過程已經明白了.然后就是配置了

eureka:
  client:
    eureka-server-d-n-s-name: relinson.com
    use-dns-for-fetching-service-urls: true
    region: region1
    eureka-server-u-r-l-context: eureka
    eureka-server-port: 9999
    prefer-same-zone-eureka: true

啟動后可以看到這種方式配置還算是成功的

免責聲明！

本站轉載的文章為個人學習借鑒使用，本站對版權不負任何法律責任。如果侵犯了您的隱私權益，請聯系本站郵箱yoyou2525@163.com刪除。

猜您在找 eureka集群基於DNS配置方式 eureka集群的兩種配置方式:配置文件方式與DNS方式 eureka 集群的實現方式？ Eureka的集群配置配置 Eureka Server 集群 Eureka集群配置 eureka集群高可用配置 SpringCloud學習之eureka集群配置 Eureka 集群高可用配置. 基於 DNS 動態發現方式部署 Etcd 集群