Clustering Axis2. Chamikara Jayalath WSO2 Inc.

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1 Clustering Axis2 Chamikara Jayalath WSO2 Inc.

2 Contents Introduction to Axis2 The problem Achieving scalability and availability Clustering solutions Solution 1 A stateless cluster Solution 2 Session affinity Solution 3 State replication Solution 4 Performance improved solution 3

3 Axis2 The latest Web services framework from Apache. Next generation of Axis1

4 Axis2 Features StAX (Streaming API for XML) based object model. Support for extending the framework. (Modules*) Web Services are self contained archives Support for many useful WS specifications (WS- Addressing, MTOM, WS-ReliableMessaging, WS- Security etc.) * Self contained archive built according to a standard. Will work as an extension to the basic Axis2 engine.

5 Axis2 - Architecture SOAP Processing Unit Axis2 Transport Receiver Transport Sender Request Handler Chain Response Handler Chain (Optional) Message Receiver Service Object Context Hierarchy Description Hierarchy Axis Configurator Message Path

6 Axis2 Architecture, contd... TransportListners Responsible for listening to transport mechanisms*, building a SOAP message out of a transport stream and feeding it into the Axis2 engine. Handlers Responsible for processing the SOAP headers. (e.g.: AddressingHandlers process WS-Addressing headers). MessageReceiver Responsible for processing SOAP body and invoking the service implementation object. TransportSender Responsible for sending response messages back to the transport stream. *A transport in Axis2 is a channel through which SOAP messages could be sent or retrieved. Ex: HTTP, SMTP

7 Axis2 Architecture, contd... Configuration hierarchy An object hierarchy to hold configuration information of the system Context hierarchy An object hierarchy to hold runtime information of the system Acts as a simplified in-memory database. Web Service authors should store their runtime information in the context hierarchy. Axis Configurator Deploys service and module archives into Axis2.

8 The problem Achieving scalability and high availability As the load increases an Axis2 server will have to be horizontally scaled by adding new servers. Most cost effective than buying expensive hardware. As you scale horizontally, probability of hardware and other failures increase. Availability is about offering a solution to address the increased risk of failure

9 The Problem, contd... How do you deal with increased service load in a reliable manner? Scalability is achieved by adding more servers Reliability is achieved by replicating functionality across two or more servers

10 Solutions Here are the solutions we hope to provide to solve the above problem. Solution 1 Stateless cluster If your services are fully stateless you can use this solution to achieve scalability and availability. Solution 2 Session Affinity If you want to obtain scalability preserving client sessions. Solution 3 Session state replication If you want to achieve both scalability and availability preserving client sessions. Solution 4 -A performance improved version of solution 3 If you want to improve the performance of solution 3 by grouping the nodes of the cluster.

11 Solution 1 A stateless cluster Achieved by configuring two or more Axis2 instances with a shared repository*. Services can be scaled by increasing the number of nodes. Services do not share any state information. So should be used only when your services are stateless. *The directory containing configuration details for Axis2 (e.g. Web Services, modules)

12 Solution 1 A stateless cluster A load balancer will have to be used for dividing incoming requests among the available Nodes.

13 Solution 1, contd... Axis2-1 Service requests Load Balancer Axis2-2 Axis2-3 Shared Repository Axis2 Cluster

14 Solution 1 - Load Balancer Possible types of Load Balancers Round robin DNS HTTPD Load Balancer Apache Synapse Other options like hardware load balancers Synapse A mediation tool which can be configured to route web services messages according to a given set of rules.

15 Solution 1 -Limitations Session based interactions are not supported

16 Solution 2 Session Affinity Provides scalability preserving client sessions. Makes the Load Balancer aware of sessions.

17 Solution 2, contd... Load Balancer will look for session IDs in incoming messages. Messages with the same session ID will be directed to the same node. Synapse will be implemented as the Load Balancer with support for sessions.

18 Solution 2, contd... Axis2-1 Synapse (Load Balancer) Axis2-2 Shared Repository Maps session Id->Node Id Axis2-3 Just like in the previous solution. The repository will be shared.

19 Solution 2 Session Types Synapse Load Balancer will be aware of various types of client sessions. e.g.: Service session* WS-ReliableMessaging sessions WS-SecureConversation sessions *A concept of Axis2 where the server generates a session Id which could be included by clients as a SOAP header. The Id is named ServiceGroupContextId

20 Solution 2 Limitations Does not support high availability. If a node fails all the session and state information that was associated with it will get lost.

21 Solution 3 State replication Will provide both scalability and high availability Nodes will share state information using a reliable group communication mechanism. Load Balancer will not have to be aware of client sessions. So different types of load balancers can be used.

22 Solution 3 - State replication Better to use an existing group communication technology (e.g. Tribes, Ricochet, JGroups). Axis2 should not be bound to a single group communication technology (A user requirement).

23 Solution 3 Proposed Solution An abstraction layer to replicate the state information of Axis2. Axis2 state information is in it's context hierarchy. The abstraction should be used to replicate the context hierarchy.

24 Solution 3, contd... Axis2-1 Service requests Load Balancer Axis2-2 Axis2-3 Shared Repository Exchange of State information using the abstraction Axis2 Cluster

25 Solution 3, contd... Each context has a property bag (a HashMap) to hold its state. So what we have to do is replicating these property bags.

26 Solution 3, contd... Interface of the abstraction layer public interface ClusterManager { //Cluster/Node initiation void init (ConfigurationContext context); //Managing contexts. void addcontext (String contextid, String parentcontextid, AbstractContext context); void removecontext (String contextid); //Managing properties void addproperty (String contextid, String propertyname, Object propertyvalue); void removeproperty (String contextid, String propertyname); void touchproperty (String contextid, String propertyname); } //Managing transactions void commit (); void abort () void begin ()

27 Solution 3, contd... Cluster/Node communication The 'init' method will either initialize the cluster or add the current node to an existing cluster. Managing contexts Whenever a context get created or destroyed, that information will be given to the ClusterManager instance using respective methods. Managing properties Whenever a property get added, removed or touched the ClusterManager instance will be informed. Managing transactions Transaction handling methods could be used when sending information to the cluster.

28 Solution 3 - Limitations Performance of the cluster could drop when the number of nodes go higher. Installing and maintaining may need more work.

29 Solution 4 Improved solution 3 Will improve the performance of solution 3 by grouping the nodes of the cluster. Each node will be sharing state with only the other nodes of its node group. Will provide both availability and scalability. Performance of the cluster will get improved since group communication messages will only be exchanged within groups.

30 Solution 4, contd... Load Balancer will be aware of client sessions. Load Balancer will direct messages of the same session into the same node group.

31 A combined solution, contd... N1 N2 N3 Axis2 Nodes Synapse Load Balancer N4 N6 N5 Maps sessionid -> NodeGroupId Node Groups N7 N8 N9

32 Solution 4 - Limitations Availability and scalability may be lesser than a solution 3 type of a cluster with the same number of Nodes. Load Balancer will have to be aware of sessions.

33 Summary Axis2- the latest Web Service framework from Apache. Clustering Axis2 For availability and scalability requirements. Solution 1 A stateless cluster Solution 2 Session affinity Solution 3 State replication Solution 4 Performance improved solution 3

Achieving Scalability and High Availability for clustered Web Services using Apache Synapse. Ruwan Linton WSO2 Inc.

Achieving Scalability and High Availability for clustered Web Services using Apache Synapse Ruwan Linton [ruwan@apache.org] WSO2 Inc. Contents Introduction Apache Synapse Web services clustering Scalability/Availability