Billing in cloud computing - StratosLive billing explained

StratosLive comes with its own billing system to bill the tenants for using the cloud. Lets have a look at the bill generation process of StratosLive. Shown below is a simple diagram to explain the base entities involved in bill generation.

There can be multiple billing engines in your environment. In StratosLive there are two of them. One is for scheduled bill generation (monthly invoice) and the other is for on-demand bill generation (interim invoice). Both these engines use a single billing database. Each of these engines have a set of handlers to be executed. These handlers can be configured via the billing-config.xml. These handlers are executed by the engine at the time of bill generation. Shown below is segment from the billing-config.xml

   

   

   

   

   

       multitenancy-billing-rules.drl

   

   

   

   

   

   

       email-billing-notifications.xml

   

What are the data used in bill generation?

• Subscription details – subscriptions of the user for the duration considered in the bill generation. There is a subscription entry for each usage plan which the user was subscribed to during the billing period
• Usage details – Usage details of the user for the month of bill generation. This includes bandwidth usage (webapp bandwidth, service bandwidth and registry bandwidth) and registry storage of the user.
• Pricing strategy – This defines how users are going to be charged for subscription and overusage. Shown below is a sample xml file which defines the pricing strategy.

10 



 10

 0 





 25 

 0.1





 2000 

 0.1 

When does bill generation happen?

As I mentioned previously, monthly invoice is generated by a scheduled task. This is achieved via Synapse scheduled tasks. When the billing manager is started (i.e. when the server starts), bill generation task is scheduled for the billing engine. This task scheduling can be configured via the billing-config.xml.

Lets go through the bill generation step-by-step. Billing engine for scheduled bill generation executes the following set of handlers.

1.SubscriptionFeedingHandler – Retrieves the subscription entries relevant to the bill generation period. For each subscription, relevant user's usage data also retrieved. Subscription entries are added to the BillingEngineContext to be used by other handlers.

2.SubscriptionTreeBuildingHandler – Goes through all the subscription in the context and arrange the subscriptions of same customer together. Creates invoices and assigns the subscriptions to them. Fills some data of the invoice such as invoice dates, payments falling under the billing period.

3.RuleHandler – Rules are used to calculate the subscription fees. Rule handler executes the rules over the billing engine context. This will assign a subscription fee for all the subscriptions in the contex.

4.InvoiceCalculationHandler – Over usage charges are calculated by this handler according to the pricing strategy define in a xml file. Total cost, total payments an carried forward values are also calculated. At this moment, there is a complete invoice for all the customers in the memory.

5.Finalizing Handler – This handler takes care of storing the invoices in the billing database.

6.EmailSendingHandler - After generating and storing the invoices, customers have to be notified. It is done by the email sending handler. When this is done you receive an email notifying you about the invoice.

Diagram below gives an idea on what happens in the first four handlers.

Scheduled vs. On-demand bill generation

These two operations are carried out by two billing engines

Scheduled generation executes two additional handlers than the on-demand generation. They are the finalizing handler and the email sending handler. When the invoice is generated on-demand, it is not stored in the database (because it is only for presenting to the user). No email notification is necessary because the invoice shown in the UI. That is the reason for FinalizingHandler and EmailSendingHandler not needed for on-demand bill generation.

Flexibility

The whole bill generation process is execution of set of handlers. If you want to add something new to the flow, you can simply write a handler. Then you need to mention that handler in the billing-config.xml for it to be executed by the engine.

Billing component will be further improved to calculate all the costs via rules. Then it will be super easy to make changes in cost items and pricing because only what we need is to edit the rule file. This avoids any code level change when it comes to changes in calculating the cost which is a huge advantage.

Billing the cloud - StratosLive invoice - What does it contain?

StratosLive is a complete Open PaaS from WSO2. It comes up with its own billing component to bill the tenants for using the cloud. If you have tried out StratosLive, you must have received a monthly invoice for using it. Although you receive an invoice it does not means StratosLive charges for everything. If you want you can sign up for a Demo account which is free or else you can sign up for a paid account with more privileges to consume resources.

StratosLive's billing is based on two parameters.

1.Subscription of the tenant – When you sign up to use StratosLive you can select a usage plan. You can change this usage plan whenever needed. There is a monthly subscription fee associated with the plans.

2.Resource usage – When you select a usage plan, there is a set of resources which can be used under that plan. If you happen to consume resources more than the amount allowed, the excess usage will be charged.

Invoice is generated on the last day of the month and you are notified via email once it is available. Shown below is a sample invoice and I'll describe what is included in it. You can view the invoice in StratosLive Manager's Home → Billing & Metering → Past Invoices.

Following information is available in the invoice.

A) Invoice number

B) Invoice period (i.e. for which time period does this invoice applicable) and Invoice date – date which the invoice was generated

C) Subscription fees for the subscriptions you have used during the period. For example if you have sticked to the same subscription there will be one entry for this. But in this sample invoice, the user has used a SMB usage plan for 5 days and then has changed it to a Demo usage plan. Therefore there are two entries for subscription fee section. It is important to notice that the subscription fee is calculated only for the number of days which you were subscribed in to it.

D) Over usage charges – At the time of bill generation, users usage data is retrieved by the billing engine and compares it with the allowed usage limits for the active subscription at that time. If the user has exceeded the allowed limit, excess usage is charged. Charging the excess usage depends on the desire of the cloud owner. For example, in the above invoice, the tenant has consumed 32MB of excess storage. But it is not being charged. Over use charges are calculated for Bandwidth and Storage. Invoice clearly mentions how much is charged for each of them.

E) Payment details within the period – If you did a payment for your previous invoice, it should clearly be mentioned in this invoice. You can see it in the sample invoice too.

F) Finally, there is a summary which includes the Brought Forward value, Total cost for this period, Total payments during this period and the Carried forward value.

G) After all those details, you get the Paypal button to pay the invoice securely.

Interim Invoice

You will not find this facility in many billing systems. But StratosLive provides you to view your cost for using it up to this moment. Interim invoice shows your costs from the last invoice date to this moment. Many cloud services only provides you the monthly invoice at the end of the month. But we provide you the invoice on demand.

If you have been charged for over using resources, you can check whether the excess usage amounts mentioned in the invoice are accurate by going through you usage report for the month. Usage report can be found at Home →Billing & Metering →Usage Report

Metering, Throttling and Billing in cloud

Usage metering is a very important area when it comes to cloud computing. No matter whether it is a public or a private cloud, PaaS provider will be interested in metering the resources consumed by tenants. Accurate metering leads to successful throttling and billing.

WSO2 StratosLive is a public cloud deployment. There needs to be a way of measuring how tenants consume cloud resources. It is necessary to measure them to control or facilitate the tenants consuming resources. StratosLive encourages tenants to make full use of it's resources. But there needs to be a control mechanism too. Billing, Metering and Throttling components are responsible for measuring resource usage, charging the tenants and controlling access to resources in StratosLive.

What is Metering, Throttling and Billing?

Metering is the base for Billing and Throttling. It measures bandwidth and storage consumed by tenants. Throttling runs its throttling rules against the metered data and takes decisions on access controlling to resources. This resources are, webapps, services, registry storage and registry items. Billing, if enabled (which is enabled in StratosLive), charges customers based on the metered data in a monthly basis. Billing considers not only the metered data, but also the usage plan which the tenant is subscribed and the pricing strategy.

Metering

What are being metered?

In StratosLive following are being metered tenant-wise.

• Webapp bandwidth – When a request is coming to a webapp hosted by a tenant and a response is sent, the amount of bandwidth consumed is metered.

• Service bandwidth – When a service hosted by a tenant is invoked and a response is received, the amount of bandwidth consumed is metered.

• Registry bandwidth – When registry resources are accessed (get/put), the amount of bandwidth consumed is metered.

• Registry storage – When artifacts are added to the registry, the amount of consumed registry storage is metered.

How they are being metered?

Webapp and service bandwidths are measured via Tomcat valves(add a link here). When the request is going through the valve, bandwidth is measured. Registry bandwidth and registry storage is measured when artifacts put/get into/from the registry.

StratosLive services (i.e. Enterprise Service Bus, Application Server) measures the above data and sends them to the Business Activity Monitor to be stored. These metered data are then summarized periodically making them available for billing and throttling components.

What data is available for tenants?

Tenants can view their monthly usage report in StratosLive Manager under the following menu.

Home → Billing & Metering → Usage Report

Shown below is a screen shot of a usage report

Throttling

Throttling component is scheduled to run throttling rules periodically and update permission of tenants on accessing/consuming various resources and stores them in the registry. There are throttling agents in each and every service. When a tenant is trying to access a webapp/service/registry item, throttling agent looks for the permission for the relevant action and decides whether to allow or discard the request. One great advantage of the throttling in StratosLive is throttling rules can be updated on the fly. StratosLive Manager provides this facility only to the super-tenant (i.e. the administrator of StratosLive). This means, if you have a private cloud setup, you have total control over throttling. Once the rules are updated via the StratosLive Manager UI, next run of the rules will be using the updated rules.


Billing

Billing (bill generation) is done on a monthly basis. Bill generation is scheduled on the last day of each month. This date can be configured as you wish. When the bill generation is completed, customers (tenants) are informed via email. They can view their invoice in StratosLive Manager Home → Billing & Metering → Past Invoices. Customers can also view their interim invoice too. Interim invoice is the invoice for the time period from last invoice to this moment. This is generated on demand and can be viewed in StratosLive Manager Home → Billing & Metering → Interim Invoice. Shown below is a sample invoice of a tenant.


Where does Billing, Metering & Throttling takes place in StratosLive?

StratosLive user base is growing day-by-day. Therefore, metering, throttling and billing operations can be very heavy. StratosLive deployment architecture makes sure that this does not affect the smooth functioning of any other services. It is done by keeping a dedicated instance for these three heavy tasks. This instance is called the Summarizer.