A Multi-tenant Architecture for Business Process

Executions

Milinda Pathirage, Srinath Perera, Indika Kumara, Sanjiva Weerawarana

WSO2 Inc.

Cloud Computing

Ability to buy computations power, storage, or execution services as an Utility, on demand.

For more details read “A View of Cloud Computing, Communications of the ACM, 2010”

Cloud Computing (contd.)

Best way to explain it is by comparing it to Electricity

Idea is we run data centers or shared servers instead of running individual servers, and share the resources. o Optimize large scale operations

and archive economics of scale.o Since the pool is big, one can

ask for resources when needed and release when not needed.

o No need for capacity planning, start small and grow as needed.

o Outsource running machines and maintenance enabling specialization.

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Cloud Offerings

Why PaaS?

IaaS only provides limited saving to someone who needs to outsource their IT functions

SaaS is great when they can be used o They are usually very specific (e.g. email, CRM ..)o If they match, then great, but if they are not, not much choice for

the user. PaaS stays in the middle ground

o Framework to host your appso Hopefully you can move your apps as it is (well not the case with

Azure or App Engine, but it is possible).

Supporting SOA in PaaS

SOA is a primary technology in the Enterprise

Many users already have SOA artifacts

Moving them to the Cloud without need for changing will be a great advantage

We want to see Cloud as yet another deployment modelo Write and test applications locallyo Even deploy it locally if neededo When you need it, you can deploy

the same artifacts in the cloud. Multi-tenancy plays a major role.

Which brings us to our Topic.

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What is Multi-tenancy ?

Many Parties share the same set of resources, while giving each an his own space

Why Multi-tenancy? Increased sharing

o Cloud shares resources across a large pool of users.

o Now sharing happens in the application level as oppose to sharing at OS level for multiple processes and sharing at HW level with VMs.

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Provide pay for what you use o Often there will be many accounts in a PaaS or a SaaS, but only a

fraction of them will be in use. o We cannot allocate runtime resource per account (disk may be ok,

as it is cheap). For example, we cannot run a VM per account. o By sharing the same server with many users, Multi-tenancy provides

much reduced runtime cost per server.

Multi-tenancy vs. Virtual Machines Multi-tenancy provides much fine

grained sharing by many applications sharing the same server.

Say there are 100k accounts, but 10k active users at a time. VM based model needs 100k VMs, which means there is a cost incurred per account.

With Multi-tenancy one server can handle many accounts, and by mixing and matching heavy and light users, Multi-tenancy can operate with much less number of servers.

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Our Earlier Works on Multi-tenancy

We provide a SOA PaaS offering called Stratos. Some of the featureso Web Service Hosting as a Service o Web Application Hosting as a Serviceo Message Mediation Execution as a Service (ESB)o Governance as a Service

Earlier publications on the topic o A. Azeez and S. Perera et al., WSO2 Stratos: An Industrial Stack

to Support Cloud Computing, IT: Methods and Applications of Informatics and Information Technology Journal, the special Issue on Cloud Computing, 2011.

o Afkham Azeez, Srinath Perera, Dimuthu Gamage, Ruwan Linton, Prabath Siriwardana, Dimuthu Leelaratne, Sanjiva Weerawarana, Paul Fremantle, "Multi-Tenant SOA Middleware for Cloud Computing" 3rd International Conference on Cloud Computing, Florida, 2010

Today’s Topic: Workflow Hosting as a Service

Key part of the SOA puzzle o Workflows provide

interoperable means of composing services together.

Still workflow technology is mostly limited to large scale organizations

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Goalso Enable users to deploy the same workflows that they run on local

machines in the Cloud without any changes and supporting the monitoring and other features in the same way.

o Supporting Multi-tenancy o Scalability

Motivating Usecases

E-Science Gateways

Scientific workflows has been identified as enabling technology for E-Science.

Idea is to let scientists visually compose workflows and run them.

There are many gateways that do this.

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However, the cost of running gateways for different domains has been high. Workflow hosting service together with Service and Web application hosting service will enable multiple science gateways to share the same infrastructure thus reducing the maintenance cost and resource sharing .

SMBs (Small and Medium size Business)

This will lower the bar of workflow use, and enable SMBs to move to the next level.

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Most SMBs can not afforded to run their own workflow technologies.

This stops them from goes to the next level.

Workflow, Service and Web hosting services can enable multiple SMBs to share the same infrastructure.

Goals of Multi-tenancy

Sharing – maximize the resource sharing across multiple tenants.

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Isolation – hide the fact other other are also in the same server. o Execution – enforce security. Make sure one tenant can’t call other

tenants executable logic. o Data – make sure one tenant can’t see other data o Performance - make sure performance is not affected by

existence of other tenants. Scale

o Server is distributed and it can handle larger load by adding more nodes.

Related works

Mitezner [5] and Shi et al.[6] introduced application templates where the system lets users customize a template workflow.

Mitezner et al. introduced a tenant context to hold execution data and isolate executions. We also use a similar concept.

Cai, Wang, and Zhou [8] have used tenant context to support multi-tenancy in Web Applications.

Anstett et al. [9] discuss challenges of bring BPEL processes to cloud. o Need changes to BPEL engineo Configuration data isolationo Avoid giving access to DBso Securing the Data in the communication

BPS Multi-tenancy Architecture

Achieving Service Execution Isolation

All executions are based on Axis2 (ODE also runs on Axis2) Axis2 have stateless executions and keep all state in a Context. So if we create different context for each tenant, they are

isolated. See Azeez et al. “Multi-Tenant SOA Middleware for Cloud

Computing” for details

BPS Multi-tenancy Architecture

BPS Multi-tenancy Architecture (Contd.)

Extends Apache ODE Has a single tenant Apache ODE Engine as the core and

added Multi-tenancy by adding a Multi-tenant process store and adding isolation at the message reception.

Parts of the architecture o A Process store per tenant, which only allows calls from that

tenanto Parent process store that provides a single process store view

across all tenant stores (to Apache ODE).

BPS Multi-tenancy Architecture (Contd.)

When a workflow is deployed by T1, it is stored in T1’s process store. Also, a service is created for the workflow and deployed within T1’s space.

When a workflow received a message, the service that receives the message perform access control and then injects it to ODE with tenant ID as a correlation property.

A implicit correlation rule together with other correlation rules routes the messages to a workflow instance.

When workflow instance access the process store, it is routed to the T1’s tenant process store.

Isolation

Data isolation is provided by the process store per tenant, which stores data in the multi-tenant registry.

Execution isolation is provided by Service isolation which enforces security on any external calls before a message is injected in to the workflow engine. After entry, isolation is provided by data isolation and workflow engine.

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Workflow engine creates a new version when a process is redeployed, and each version is isolated. So multiple users can have workflows with the same name in the workflow engine.

Isolation (Contd.)

Performance isolation is a challenging issue. o We currently relay on monitoring and auditing where we can kill

CPU hogging processeso We are exploring the possibility of changing the priority of CPU

hogging processes in the work queue.

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Scaling

Run multiple BPS nodes in a clustero Tenants are partitioned across BPS nodeso Fronted by a load-balancer which is aware of tenants and

processes

Performance

Setup Multi-tenant and non-multi-tenant versions Run 200 workflows from each client Overhead is minimal

o MT supports only add few additional lookups and checkso Java Security does not come in to play as we do not run user

provided code.

How does it make a difference?

Supporting Workflow Hosting as a Serviceo Bringing down the cost of

using workflowso Increasing the sharing in the

cloud Multi-tenant BPS in private

Cloud to support multiple departments for improve resource sharing.

As a test environment and an education medium

Super tenant workflows o Workflow store model (like

App Store) to sell workflows.

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Conclusion

We proposed an architecture for supporting Multi-tenant Business Process Engine o We layered this on top of our earlier works on Service Multi-

tenancy and Data Multi-tenancy. o We discussed data and execution isolation.

We have realized the architecture on top of WSO2 BPS, which is an extension of Apache ODE

Multi-tenant business process engine enables end-users to deploy their current BPEL workflows running on their machine without any changes.

It only introduced a minimal overhead It is currently available for free from cloud.wso2.com

Questions?