dubbo-- High Availability

A, zookeeper downtime

　　zookeeper registration center downtime, you can also consume services exposed dubbo

　　Robustness:

Monitoring center shoot down does not affect the use, but the loss of part of the sampling data
After the database dawdle away, we can still provide service registry list queries by caching, but you can not register the new service
Registry peer cluster, after Renyiyitai dang off, will automatically switch to another
After shoot down all the registry, service providers and service consumers can still communicate through a local cache
Service provider stateless, after Renyiyitai shoot down, does not affect
After all the service providers dawdle away, will not be able to use the service consumer applications, and unlimited reconnection waiting for service providers recovery

Two, dubbo Direct

　　Development and testing environment, usually need to bypass the registration center, only testing service provider designated. In this case, you may need direct point to point connection, the service provider will ignore list provider registered provider. A configuration of the interface point, does not affect the B interface to get a list from the registry.

　　2.1 with xml configuration

<dubbo:reference id="xxxService" interface="com.alibaba.xxx.XxxService" url="dubbo://localhost:20890" />

　　2.2 Configuration -d

　　Add the -D parameter mapping service address to the JVM startup parameters:

java -Dcom.alibaba.xxx.XxxService=dubbo://localhost:20890

　　2.3 .properties configuration file (Please refer to the examiner network)

Three, dubbo load balancing in a cluster configuration

　　dubo provides a number of strategies used to balance the cluster load balancing, these strategies default random.

　　3.1 Random LoadBalance random load balancing

Mess, according to the weights set to random probability.
The probability of collisions in a high portion, but the larger call volume, the more evenly distributed. When using heavy weights based on the probability distribution is the same, which also helps to dynamically adjust the right provider of weight.

　　3.2 the RoundRobin LoadBalance polling Load Balancing

Round co-advisor barrels, use weight to determine robin cycle rate.
Flow to slow the provider may cause request accumulation, for example, if there is one provider at a very slow speed to process the request, but it is still effective, which means it can receive requests normally. According to Roundrobin strategy, users will continue to send a request to a predetermined speed providers, do not know the poor state suppliers. Finally, we will get a lot of requests on this unhealthy provider.

　　3.3 LeastActive LoadBalance least active load balancing

The least active activity based on a stochastic mechanism, activesmeans consumers but the numbers have not yet returned request has been sent.
Slower provider will receive fewer requests, the provider because slower higher actives.

　　3.4 ConsistentHash LoadBalance continuous hash load balancing

Request consistency Hash, the same parameters are always sent to the same provider.
When a station linked to the provider, the original request sent to the provider, based on the virtual node, in equal shares to other providers, will not cause dramatic changes. Algorithms See: http: //en.wikipedia.org/wiki/Consistent_hashing
By default only the Hash first argument, if you want to modify, configure <dubbo: parameter key = "hash.arguments" value = "0,1" />
160 parts by default virtual node, if you want to modify, configure <dubbo: parameter key = "hash.nodes" value = "320" />

　　3.5 Configuration

　　　　3.5.1 Server service levels

<dubbo:service interface="..." loadbalance="roundrobin" />

　　　　3.5.2 Customer Service Level

<dubbo:reference interface="..." loadbalance="roundrobin" />

　　　　3.5.3 server methods class

<dubbo:service interface="...">
    <dubbo:method name="..." loadbalance="roundrobin"/>
</dubbo:service>

　　　　3.5.4 client class method

<dubbo:reference interface="...">
    <dubbo:method name="..." loadbalance="roundrobin"/>
</dubbo:reference>

Fourth, service degradation

　　4.1 What is a Service downgraded

　　When the server pressure surge, according to the actual business situation and flow of some services and pages do not deal with or have easy ways to change the policy process, freeing server resources to ensure the normal operation of the core transaction or efficient operation.

　　Service may be temporarily shielded by non-critical service degradation, and return policies defined for it

　　Dynamic configuration rules will be published to the registry:

RegistryFactory registryFactory = ExtensionLoader.getExtensionLoader(RegistryFactory.class).getAdaptiveExtension();
Registry registry = registryFactory.getRegistry(URL.valueOf("zookeeper://10.20.153.10:2181"));
registry.register(URL.valueOf("override://0.0.0.0/com.foo.BarService?category=configurators&dynamic=false&application=foo&mock=force:return+null"));

Configuration mock=force:return+nullThis means that all calls to the service will have a direct return NULL value, without remote call. Commonly used to reduce the impact of certain non-critical slow service.
In addition, you can also change the configuration to mock=fail:return+nullafter the call fails, you'll get a null value. Remote user attempts to call, if the call is successful, will get real results; If the call fails, a null value will be obtained. Commonly used to tolerate certain non-critical services.

Five, fault-tolerant cluster

　　When a cluster call fails, dubo offers a variety of fault-tolerant solutions, the default Failover Cluster (failover retry) .

　　5.1 fault-tolerant cluster mode

　　 1.Failover Cluster

　　　Automatic switching failure when a failure occurs, retry other servers. Usually used for read operations, but retry will bring a longer delay. Through retries = "2" to set the number of retries (excluding the first).

　　　Number again re-arranged as follows:

<dubbo:service retries="2" />

<dubbo:reference retries="2" />

<dubbo:reference>
　　<dubbo:method name="findFoo" retries="2" />
</dubbo:reference>

　　2.Failfast Cluster

　　　Quick failure, only to initiate a call immediately fails error. Write operations commonly used in non-idempotent nature, such as the new record.

　 3.Failsafe Cluster

　　　Security failure, abnormal, direct ignored. Typically operable to write audit logs.

　 4.Failback Cluster

　　　Automatic recovery fails, background records failed request, the retransmission timer. Typically a message notifying operation.

　 5.Forking Cluster

　　　Call multiple servers in parallel, that is as long as a successful return. Typically used for higher real-time requirements of a read operation, but more services need to waste resources. May = "2" to set the maximum number of parallel through the forks.

　 6.Broadcast Cluster

　　　Calling all broadcast providers, one by one call, Renyiyitai error is an error. Typically used to notify all providers such as cache or log updates the local resource information.

　5.2 Cluster-Mode Configuration

　　Provides services in the following examples and consumers cluster configuration mode

<dubbo:service cluster="failsafe" />

<dubbo:reference cluster="failsafe" />

dubbo-- High Availability

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