Environment setup


  • JDK 7 or later installed

  • Maven 3.5.2 or later installed

  • Git 2.15.1 or later installed


The Kill Bill projects can be imported into the Eclipse IDE as long as the m2e plugin is installed. Recent versions of the Eclipse IDE for Java EE Developers come with this plugin already.

Some of the Maven plugins used may not be available to m2e, however, and the projects will not import completely. To work around this issue, the Eclipse Preferences > Maven > Lifecycle Mappings configuration can be updated to include mappings like the following:

<?xml version="1.0" encoding="UTF-8"?>


Kill Bill is a standard Maven project. Simply run the following command from the project root directory:

mvn clean install -DskipTests

On the first build, Maven will download all the dependencies from the internet and cache them in the local repository (~/.m2/repository), which can take a considerable amount of time. Subsequent builds will be faster.

Once built, you can start Kill Bill by running:

./bin/start-server -s


By default, Kill Bill will expect a MySQL database. To switch to PostgreSQL:

  • Create a killbill user and database (verify connectivity with psql -h -U killbill -p 5432):

create USER killbill;
\password killbill;
  • Create the schema:

./bin/db-helper -a create  --driver postgres -u killbill -p killbill
  • Modify the profiles/killbill/src/main/resources/killbill-server.properties:




The base pom.xml (org.kill-bill.billing:killbill-oss-parent) defines all of the dependencies required by Kill Bill. If a -SNAPSHOT version is specified (e.g. 0.141.74-SNAPSHOT), this means some dependencies haven’t been released yet and you need to build them locally, before being able to build Kill Bill.

Typically, the following repositories need to be built in order:

Navigating the Kill Bill codebase

It can be quite daunting to start poking around the Kill Bill codebase, as the code is scattered over various repositories. Here is a primer on how to get started.

Core system

The following blog posts can help provide more context on the Kill Bill architecture:


Date, Time and Timezone

A few general concepts around time in Kill Bill:

  • Kill Bill’s granularity is the day, and as a result the system will not invoice for portions of a day.

  • Each account in Kill Bill has a default timezone and that timezone is used throughout the system to be able to convert a DateTime into a Date into the account Timezone.

  • Kill Bill will internally use UTC for all its Datetime manipulation, but any Date information is interpreted as a Date in the account timezone.

Mysql Date, DateTime, Timestamp

We are only relying on date and datetime which are not sensitive to the MySQL timezone setting:

  • Datetime: Storing a Datetime value into MySQL relies on datetime which is independent of the mysql time_zone. It is stored as a UTC value, and the selected value is always the same, regardless of the MySQL timezone.

  • LocalDate: Storing a LocalDate value into MySQL relies on date which is also independent of the MySQL time_zone.

System Configuration

From an operation point of view, there are different places where timezone may be set:

  1. Server on which Kill Bill runs

  2. JVM setting

  3. Database server

It is required to have Kill Bill runs in UTC for correct serialization of DateTime/LocalDate. Actually, in Java, there is no UTC timezone setting but instead GMT. In a first approximation, we will consider those identical, even though they are not and could lead to some rare issues.

When Kill Bill starts, it will override the default timezone if this one was specified as a system property with something different than GMT. The code will log a WARN message and proceed to do so, to avoid issues later down the road.


Kill Bill APIs that accept dates as an argument will allow for the following:

  • A fully qualified Datetime (a point in time)

  • A Date

If there is a need to convert from a Datetime to a Date, the conversion will occur by specifying the account timezone, so the resulting Date is as seen by the customer. This would for instance be the case when triggering a future invoice by specifying a target Datetime.

If there is a need to convert from a Date to Datetime, this is obviously more subtle as we can’t infer the additional precision to compute the time. The Date is always interpreted to be a Date as seen by the customer, that is in the account timezone.

The system will use the reference time on the account in such a way that converting back from that fully qualified Datetime using the account timezone would give us back the original Date provided.

Multiple changes in a day

So what happens if a user is making several subscription changes within the same day?

In the default mode, Kill Bill will react to changes immediately and trigger a new invoice for each change, which in turn might result in a charge.

Let’s consider the following case, where there exists 3 monthly plans (Bronze, Silver and Gold), ordered by ascending price:

  • Initially, the customer is invoiced for the Bronze, from january 1st to feb 1st. By default a payment would also be made.

  • On January 1st again, the customer changes its mind and moves to Silver. A new invoice is generated that will credit the full month — including the day of january 1st — and the new plan is now invoiced from january 1st to february 1st and the credit generated is immediately used, so in the end the customer is really only invoiced for the difference of the price between the 2 plans; Additionally, a new payment is made for that amount.

  • If now the customer changes its plan on Jan 2nd, the portion from January 1st to January 2nd will be invoiced for the Silver plan and the portion from January 2nd to February 1st will be invoiced for the Gold plan.

From an entitlement point of view, the system will reflect the current plan and therefore two different calls to retrieve the plan information on January 1st may lead to different results since there was a change of plan during that day.

Adding a new cache


  1. Create a new CacheType in @Cachable

  2. Create a new cache loader in org.killbill.billing.util.cache. Make sure to extend BaseCacheLoader and reference your CacheType via getCacheType(). The loader should also be marked as @Singleton.

  3. Register your new cache loader in the constructor of EhCacheCacheManagerProvider

  4. Configure your new cache in ehcache.xml

You’re all set! To start caching your SqlDao calls, mark your method as @Cachable and use @CachableKey in the method arguments to create the cache key.

Families of Caches

There are different types objects cached in Kill Bill:

  • Id mapping caches (UUID → Long); for e.g accountRecordId

  • Audit logs

  • Higher level resources (Tenant Catalog, Tenant OverdueConfig)

Id mapping caches

The information cached is immutable and does not have to be synchronized across Kill Bill instances; in the worst case, we have a cache miss on a specific instance, and then the cache will end up being populated.

The mapping info is implemented in DefaultNonEntityDao; the call first provides a CacheController which will look for cached info, and if not found call the corresponding CacheLoader. This one in turn will call back the DefaultNonEntityDao with a null CacheController, which will result in making the call to the database and populate the cache.

Also, there is some special logics in EntitySqlDaoWrapperInvocationHandler that will populate the cache when objects get created — when they get retrieved actually the first time using getById. Since the pattern in Kill Bill is to retrieve store information using getById after object was created, this ends up populating the mapping cache.

Audit logs

The information cached here is mutable and needs to be synchronized across different instances of Kill Bill. This has not been implemented.

The logics to cache information happens in EntitySqlDaoWrapperInvocationHandler.

Higher level resources

The information cached here is mutable and needs to be synchronized across different instances of Kill Bill. The code path is a bit more complex because:

  • We are caching higher abstraction than what is actually inserted in the raw tables; for e.g we store strings in the tenant_kvs table for the per tenant catalog and yet we cache the VersionedCatalog so that it does not have to rebuilt on each call.

  • We need to take care of the multi-node implementation which means we need some form of cache invalidation.

There are different pieces for that puzzle — let’s look at the catalog, but this is similar to overdue for the overdue config xml files:

In the catalog module, the service registers the CacheInvalidationCallback with the tenant module at INIT_SERVICE; this is required to make sure the tenant module which does not have dependency on the catalog can call catalog specific code to invalidate the entries when it detects some modifications. The per tenant catalog are cached in the catalog module in the EhCacheCatalogCache. The EhCacheCatalogCache offers the api to load and invalidate the cache.

In the util module, we find the TenantCatalogCacheLoader; this is symmetrical with any other types of cache we discussed. The TenantCatalogCacheLoader is the one making the call to load information from disk. In that case this is slightly more complex because the TenantCatalogCacheLoader needs to return a higher level abstraction than the raw strings stored in disk, and the conversion requires some logic that exists in the catalog module. Since util does not have any dependency on the catalog module, the catalog module needs to also pass a LoaderCallback which knows how to make the transformation. Also note that the raw strings are loaded using the TenantInternalApi as opposed to just making a DAO call since the raw information lives in the tenant module.

The tenant module is where the raw information is stored. It provides 2 sets of APIs:

  • An TenantInternalApi which is used internally to initialize CacheInvalidationCallback and retrieve information without going through the lower level cache magic in EntitySqlDaoWrapperInvocationHandler.

  • A TenantUserApi which allows to store the raw data addTenantKeyValue(). In addition it contains also a small service that listens periodically to broadcast notifications when a catalog for a given tenant has changed. This is implemented in TenantCacheInvalidation and the goal here is to invoked the invalidation callback.

Adding a new plugin API

Kill Bill supports multiple plugin APIs, which goal is to customize the system or interact with third party providers.

The purpose of this doc is to help with the engineering effort required to add a new plugin API, and is not an exact exhaustive list of recipes to apply.

Overview of the changes

The following areas have to be considered when adding a new plugin API:

  • Plugin Apis: Add the new maven module into the repo https://github.com/killbill/killbill-plugin-api to match that new API, and define all the abstractions and APIs

  • Kill Bill platform changes:

    • Modify the OSGI magic to auto-detect plugins of that new type when they are discovered

    • Add JRuby support

  • Kill Bill Core changes:

    • New Plugin API Wiring

      • Add the Guice binding in the component module

      • Make sure it is injected at the right place (where it needs to be used)

    • Plug the new plugin API into the code (modify the code to now call that API where it makes sense)

    • Decide/Implement mechanism to use if there are multiple plugins of that type registered

  • Ruby:

  • Tests:

    • Beatrix tests: add a new beatrix test that will test that API (and verify the plumbing is correct as well)

    • Write an integration test that will use the ruby test plugin

Gory details

Let’s assume we are trying to add new plugin API called Foo, in a Kill Bill module called Bar. In the case of the PaymentPluginApi, Foo = Payment, and the module Bar = https://github.com/killbill/killbill/tree/master/payment.

Platform Changes

The OSGI magic to register new plugins of a given type occurs in KillbillActivator:

The following would need to be added in the KillbillActivator

@Inject(optional = true)
public void addFooPluginApiOSGIServiceRegistration(final OSGIServiceRegistration<FooPluginApi> fooProviderPluginRegistry) {

Additionally, there is Java platform piece of code that needs to be written to support Ruby plugins:

  1. In JRubyActivator, define new KILLBILL_PLUGIN_JFOO = "Killbill::Plugin::Api::FooPluginApi", and modify startWithContextClassLoader to support Foo

  2. Create new class JRubyFooPlugin

  3. Add Guice binding where necessary

Kill Bill Core Changes

This section is a bit harder to describe as it depends on the plugin type, and what the code expects to do with that plugin API. But the main pieces are:

  1. Create a new DefaultFooProviderPluginRegistryProvider implements Provider<OSGIServiceRegistration<FooPluginApi>>

  2. Create new DefaultFooProviderPluginRegistry implements OSGIServiceRegistration<FooPluginApi>

  3. Add Guice bindings in the module for DefaultBarModule

  4. Inject the new registry OSGIServiceRegistration<FooPluginApi> where it is needed, that is at the place where the current code will need to interact with that new FooPluginApi (See example in InvoicePluginDispatcher for InvoicePluginApi)

  5. Define the mechanism to decide what happens when there are multiple plugins registered for that api. The code could walk through all plugins (ordering, aggregation or stop at first one that replies, …​), use some property or other mechanism to pick a specific plugin. For instance:

    • PaymentPluginApi: The Payment code will use the PaymentMethod associated the payment call to decide how to route to the correct plugin

    • InvoicePluginApi: The Invoice code will loop through all plugins and aggregate the results

  6. Potentially add some NoOpFooProviderPluginProvider and NoOpFooPluginApi if Kill Bill needs to ship with an embedded default plugin by default, or if those are needed for tests

Beatrix tests

Take a look at TestWithTaxItems which tests the InvoicePluginApi

Ruby Framework

  1. A new class foo.rb must be defined similar to invoice.rb for the InvoicePluginApi and add require in killbill.rb

  2. Regenerate the auto-generated plugin classes using the generator

Plugin Compatibility with API changes

It would very convenient to make backward compatible API changes to a given stable Kill Bill version (e.g 0.22.x), but in order to do that we need to understand what is the impact on existing plugins (that were build prior such api change). This document tracks some investigation made to answers this question.

Exporting a new API Class

At the time of this writing the OverdueApi is not exported to plugins — but it should.

In this experiment, I modified killbill-platform to export OverdueApi, and checked what was happening:

Starting any of our Ruby plugin would not work.

caused by: org.jruby.exceptions.RaiseException: (NameError) uninitialized constant Killbill::Plugin::Api::OverdueApi
	at RUBY.load_missing_constant(/var/tmp/bundles2/plugins/ruby/killbill-stripe/4.1.0/ROOT/gems/gems/activesupport-4.1.16/lib/active_support/dependencies.rb:520)
	at RUBY.const_missing(/var/tmp/bundles2/plugins/ruby/killbill-stripe/4.1.0/ROOT/gems/gems/activesupport-4.1.16/lib/active_support/dependencies.rb:180)
	at org.jruby.RubyModule.const_get(org/jruby/RubyModule.java:2648)
	at RUBY.to_class(/var/tmp/bundles2/plugins/ruby/killbill-stripe/4.1.0/ROOT/gems/gems/killbill-8.3.0/lib/killbill.rb:12)
	at org.jruby.RubyArray.each(org/jruby/RubyArray.java:1613)
	at org.jruby.RubyEnumerable.inject(org/jruby/RubyEnumerable.java:866)
	at RUBY.to_class(/var/tmp/bundles2/plugins/ruby/killbill-stripe/4.1.0/ROOT/gems/gems/killbill-8.3.0/lib/killbill.rb:11)

Adding a new API Method On a KillbillApi

All the KillbillApi files are creating through Guice AOP proxy (in order to intercept the calls and verify permissions). We will run 2 experiments

API file not used by the plugin

In this experiment, i added a new method in the Entitlement class and started a a ruby payment plugin (e.g stripe), and verified the plugin loads fine and and work as expected.

API file is used by the plugin

In this experiment, I added a new method in the the PaymentApi class, and verified that plugin loads fine and and work as expected. In addition, i made sure, such plugin calls a method from that api (e.g getPayment()), and that such call works as expected.

The test has been run both using a ruby plugin (stripe) and a java plugin (adyen).

Adding a new API method on a non KillbillApi

Some of our apis are embedded in our objects (e.g Entitlement). Such implementation are not created through Guice (and not using AOP) but instead are regular POJO, so it is important to validate those cases as well.

API file not used by the plugin

Skipped: (see next case)

API file is used by the plugin

In this experiment, i verified that adding a method on the Entitlement API, would not prevent the plugin to first retrieve Entitlement objects and second make API calls on this object.

I ran the experiment using the adyen plugin. I also tried using stripe plugin but could not complete it because of this issue.


It seems like adding new API methods to either our KillbillApi objects or other API interface is well handled by plugins, in the sense they keep working as expected without having to be regenerated. Of course, such new APIs are not available to the plugins until they get rebuilt.


Summary of the steps (and gotchas) to release Kill Bill.


A Kill Bill version has major, minor and patch numbers:

  • major is currently locked at 0

  • even minor numbers are reserved for stable releases (production ready)

  • odd minor numbers are reserved for development releases (APIs and Plugin APIs can change)

While plugins can use their own versioning scheme, official plugins have major, minor and patch numbers:

  • major tracks specific Kill Bill minor releases (e.g. 1.x.y for 0.14.z, 2.x.y for 0.15.z, 3.x.y for 0.16.z, etc.)

  • minor are used to track large changes in the plugin (e.g. gateway API version change)

Kill Bill Release


  • All code should be checked-in

  • All tests should pass on both the MySQL and Travis profiles:

mvn clean install -Pmysql
mvn clean install -Ptravis
  • Take a look at CircleCI

Documentation updates

  • Update the NEWS file with GitHub issues closed for that release and summary of important changes or bug fixes. You can browse the commits since the latest tag via:

git log $(git describe --tags $(git rev-list --tags --max-count=1))..
  • Create a release page. While the NEWS file is geared towards developers, the release notes are meant for users upgrading. Mention JAX-RS and DDL changes, new features, etc.

  • Update killbill-server-update-list.properties in killbill and killpay with a link to these release notes


  • To release, in each Java repo: mvn release:clean && mvn release:prepare && mvn release:perform

  • The order of release is:

    • killbill-api

    • killbill-oss-parent

    • killbill-plugin-api

    • killbill-oss-parent

    • killbill-commons

    • killbill-oss-parent

    • killbill-plugin-framework-ruby (with code regenerated)

    • killbill-currency-plugin-test (with update killbill gem)

    • killbill-notification-test-plugin (with update killbill gem)

    • killbill-payment-test-plugin (with update killbill gem)

    • killbill-platform (updated with the latest plugins)

    • killbill-oss-parent

    • killbill

  • If JAX-RS was changed, regenerate the client libraries and update Kaui.

  • Update killbill-docs, including XSD and DDL files in the branch gh-pages.


  • To re-run a release:perform of an arbitrary tag:

mvn -DconnectionUrl=scm:git:[email protected]:killbill/killbill.git -Dtag=your_tag release:perform
  • If release:perform fails because of Sonatype issues during the 'Closing staging repository…​' stage, wait between 30 and 40 minutes - the operation should finish in the background. If it doesn’t and/or the repository is dropped, try the following switches:

mvn -DkeepStagingRepositoryOnFailure=true -DkeepStagingRepositoryOnCloseRuleFailure=true -DautoReleaseAfterClose=true -DstagingProgressTimeoutMinutes=20 -DconnectionUrl=scm:git:[email protected]:killbill/killbill.git -Dtag=your_tag release:perform
  • If the timeout happens during the 'Remote staging repositories are being released…​' stage, wait again between 30 and 40 minutes - the operation should finish in the background. If it doesn’t, try going to the UI and close it.

  • If the release fails with signature errors, e.g.:

Waiting for operation to complete.......................................

[ERROR] Nexus Staging Rules Failure Report
[ERROR] ==================================
[ERROR] Repository "comning-1234" failures
[ERROR]   Rule "signature-staging" failures
[ERROR] *** Invalid Signature: '/com/ning/billing/killbill-beatrix/0.3.6/killbill-beatrix-0.3.6-tests.jar.asc' is not a valid signature for 'killbill-beatrix-0.3.6-tests.jar'.
[ERROR] *** Invalid Signature: '/com/ning/billing/killbill-beatrix/0.3.6/killbill-beatrix-0.3.6-test-sources.jar.asc' is not a valid signature for 'killbill-beatrix-0.3.6-test-sources.jar'.
[ERROR] *** Invalid Signature: '/com/ning/billing/killbill-osgi-bundles-test-payment/0.3.6/killbill-osgi-bundles-test-payment-0.3.6-jar-with-dependencies.jar.asc' is not a valid signature for 'killbill-osgi-bundles-test-payment-0.3.6-jar-with-dependencies.jar'.

keep re-trying to close (maybe try the nexus-staging:release goal manually). In my testing, you need N numbers of retries, where N is the original number of invalid signatures (after each run, you should have fewer and fewer errors). Alternatively, you can follow the steps here. * If you are having some issues and need to (re-)upload all the artifacts, you can do it manually: * Go in the checkout/target directory and run jar -cvf bundle.jar project.pom project.pom.asc project.jar project.jar.asc …​. where project is the name of your repo and include as many artifact with their signature as you have * Then go under 'Staging Upload' and select 'Upload Mode' = 'Artifact Bundle', and select the bundle you just created

An example of a script for the killbill-platform repo to generate the bundle.jar for each modules, which can then be updated later by hand:

for m in platform-api base lifecycle osgi-api osgi osgi-bundles platform-test server; do RES=""; cd $m/target; for i in `ls | grep asc`; do base=`echo $i | sed s/.asc//`; RES="$RES $base $base.asc"; done; rm -f bundle.jar; jar -cvf bundle.jar $RES;  cd ../..; done