making everything better with osgi - a happy case study in building a really nice runtime - h...

Making everything better with OSGi

a happy case study in building a really nice runtime

Holly Cummins cumminsh@uk.ibm.com

@holly_cummins

Let’s talk about WebSphere.

Awesome capabilities…

… for production.

For development, historically not so well-suited.

History

WebSphere Application Server (the full profile) has been around since 1998

History

forever

Big codebase

History

forever

Big codebase

Big customer base

History

forever

Big codebase

Big customer base

Big workloads

History

forever

Big codebase

Big customer base

Big workloads

… Big inhibitors to massive change

History

forever

Big codebase

Big customer base

Big workloads

History

This is not a complaint.

This is a problem we arehappy to have.

forever

Big codebase

Big customer base

Big workloads

History

This is not a complaint.

This is a problem we arehappy to have.

But it is still a problem.

forever

Code that has been around forever…

No matter how good you are, or how smart you are

If your code lives long enough, and is used enough, it ends up looking like…

dragons

Especially code that has roots

going back to late ‘90s…

By Steve Collis from Melbourne, Australia [CC-BY-2.0 (http://

creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

How do you manage dragons?

Clever WebSphere architects

Clever WebSphere architects OSGi

OSGi and WAS: The first pass…

OSGi was included in WAS v6.1, in 2006

Went from lots of arbitrary jars to a few bundles

Achieved some modularity enforced by OSGi

We did not use or expose OSGi services

Compatibility constraints: WAS is the bottom of the stack

Assumptions about resource initialization and availability

Entrenched dependencies between some core elements

Did that fix everything?

Not quite.

Did that fix everything?

By Steve Collis from Melbourne, Australia [CC-

BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

What if… If we could start over, what would we want?

Developer-friendly

Simple

Developer-friendly

Simple

Dynamic

Developer-friendly

Simple

Dynamic

Light-weight

Developer-friendly

Simple

Dynamic

Light-weight

Composable / Flexible

Developer-friendly

Simple

Dynamic

Light-weight

Extensible

Developer-friendly

Simple

Dynamic

Light-weight

Extensible

selectable content

clear API/SPI runtime/app

isolation

human usable configuration

runtimeonly

some combination oftechnologies

!app-centered

everything

What if…

grokable config

provisioning

What if…

grokable config

provisioning

runtimeonly

!app-centered

everything

How do we do this?

What if… runtime

!app-centeredeverything

And yet allow this?

no restarts

What if…

And for crying out loud, can we prevent THIS?!

runtime3rd party

bundleB

systembundle

What if…

runtime3rd party

bundleB

systembundle

Application

What if…

runtime3rd party

bundleB

systembundle

Application

What if…

runtime3rd party

bundleB

systembundle

Application

The egg problem

“Create a light-weight profile of WebSphere that starts in under 2 seconds… Don’t break any eggs”

— Ian Robinson (cleverest WebSphere architect)

The egg problem

“Create a light-weight profile of WebSphere that starts in under 2 seconds… Don’t break any eggs”

— Ian Robinson (cleverest WebSphere architect)

By miya (miya's own file) [CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

OSGi maturity model

OSGi maturity modelLevel 1: Ad Hoc

Level 2: Modules

Level 3: Modularity

Level 2: Modules

Level 3: Modularity

Level 4: Loose coupling

Level 2: Modules

Level 3: Modularity

Level 5: Devolution

Level 2: Modules

Level 3: Modularity

Level 5: Devolution

Level 6: Dynamism

Level 2: Modules

Level 3: Modularity

Level 5: Devolution

Level 6: Dynamism

Level 7: Peter Kriens

Level 2: Modules

Level 3: Modularity

Level 5: Devolution

Level 6: Dynamism

Websphere Full Profile

Level 2: Modules

Level 3: Modularity

Level 5: Devolution

Level 6: Dynamism

Websphere Liberty Profile

Dealing with our legacy

We needed a new kernel

Used the new base to re-group…

Lots of code still common with full profile

Wrap/Shim: New face on old code

Patch: tweak and replace bits where necessary

Building a kernel from scratch

OSGi-based for all the reasons

First-class use of OSGi services

Must react to configuration changes

Runtime composition on-the-fly

Bundle manifests

Bundle manifests? What manifests?We use Eclipse .classpath to

Determine project build order

Generate ant classpath

Bnd takes care of the rest

Declare services using annotations

Bnd makes overrides really easy

Useful when integrating legacy code

Bundle manifests? What manifests?We use Eclipse .classpath to

Determine project build order

Generate ant classpath

Bnd takes care of the rest

Declare services using annotations

Bnd makes overrides really easy

Useful when integrating legacy code

New developers need to have almost no awareness we’re

ConfigurationSettled on XML for configuration format

Ubiquitous

Expressive

BUT, for simplicity:

single file

usable defaults

ConfigurationComposable system requires composable configuration:

Individual components own their config

No centralized repository

No externally defined global config model

No externally defined global config modelConfiguration Admin and Metatype

- job done

No externally defined global config modelConfiguration Admin and Metatype

- job mostly done

Metatype Equinox impl + extensions

Uniform validation of user input

Define configuration and constraints in one place, it gets used everywhere else.

We favor metatype.xml for this reason

Custom namespace for additional types and validators

ibm:type — duration, location, password

pid/reference

human readable: 1h30m converted to unit of

choice

pid/reference

choiceused by developer tools to help prompt for the right kind of

path: file vs. url

pid/reference

choiceused by developer tools to help prompt for the right kind of

path: file vs. url

type=“String” ibm:type=“password”

The value is a “SerializedProtectedString”,

which is not a String.

Using OSGi Services…

BlueprintDeclarative Services

yes, there are others. We focused on these two.

Using OSGi Services… Who in their right mind wants to manage OSGi services themselves??

Exactly. NOBODY.?

Declarative ServicesWe chose DS for two main reasons:

Timing: Blueprint and Aries were just getting started

Integration with Configuration Admin and Metatype!

Config injected as one unit

activate/modified/updated methods

Service instance creation based on metatype-declared factory pid

DS target filters can be set via configuration

DS is AWESOME!

DS is a central part of the Liberty runtime

CA + M + DS = “magic”We do insane things with config-derived target filters

Our runtime would not be what it is without DS in the middle of it

But …

Remember this?We need to prevent

runtime3rd party

bundleB system

bundleA

Application

Package privacy

OSGi lets you keep your internals private.

Package privacy

Your externals are public.

Package privacy

PublicPrivate

Package privacy

PublicPrivate

Granularity

bundle C

bundle Abundle B

Granularitybundle D

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle Jbundle O bundle P

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

Granularitybundle D

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

Wait a minute, it wasn’t supposed to be that

public …

Granularitybundle D

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

Wait a minute, it wasn’t supposed to be that

public …

Granularitybundle D

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

Granularitybundle D

bundle G

bundle M

bundle K

le Jbu

ndle O

bundle M

bundle C

Granularitybundle D

bundle G

bundle M

bundle K

le Jbu

ndle O

bundle M

bundle C

le BWhat bundles do I

actually need?

Granularitybundle D

bundle G

bundle M

bundle K

le Jbu

ndle O

bundle M

bundle C

actually need?

Could I just have an archive, please?

Granularitybundle D

bundle G

bundle M

bundle K

le Jbu

ndle O

bundle M

bundle C

actually need?

Could I just have an archive, please?

This is not a new requirement

Lots of attempts to solve this problem

Eclipse features

Equinox composite bundles

Eclipse features

Apache Aries Enterprise Bundle Archives (.ebas)

Eclipse features

Apache Aries Enterprise Bundle Archives (.ebas)

Liberty features (mark 1)

OSGi Subsystems are AWESOME

A new(ish) OSGi standard

Liberty uses the Apache Aries implementation

Granularity

Package isolation

Granularity

Package isolation

Packaging

Granularity

Package isolation

Packaging

Granularity

Package isolation

Packaging

Granularity

Package isolation

Packaging

When better boxes is not enoughbundle D

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

bundle M

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

bundle M

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

bundle M Extension

bundle F

bundle E

bundle G

bundle H

bundle M

bundle N

bundle I

bundle K

bundle N

bundle L bundle M

bundle Q

bundle C

bundle Abundle B

Resolver hook

bundle M Extension

Sophisticated package visibility

Features explicitly declare API and SPI packages (IBM-* metadata in the feature manifest)

Isolation between API/SPI, apps/extensions/runtime is enforced in a few ways:

Subsystems (the Aries impl) for OSGi Applications (API)

Resolver hooks and/or Eclipse Regions for isolation between runtime, extensions (SPI), and containers (API).

Provisioning

Dynamically install features (subsystems) based on configuration

Provisioning

Adding or removing features …

Provisioning

installs or uninstalls bundles…

Provisioning

which adds or removes configurations…

Provisioning

which triggers the creation or removal of services!

Provisioning

which triggers the creation or removal of services!

No restart needed. !

#really

Did we get rid of all the dragons?

By Abraham (Own work) CC-BY-3.0 via Wikimedia Commons

The OSGi dragon

What version should this be?

What version should this be?This is ALWAYS a hard problem in any non-trivial evolving system

OSGi just makes the problem more obvious

Semantic versioning is …

Beautiful

Insufficient

Beautiful

Insufficient

Our developers never touch versions

Beautiful

Insufficient

Our developers never touch versions

That’s what a release team is for :)

How do I interact with X?Let DS do it. Really.

DS is excellent at managing non-trivial service dependencies

It is very unlikely that you will be able to do better— just let DS do it. That means:

Don’t register services inside a component

Don’t manage references inside a component

Why is my test failing intermittently ?

Because something hasn’t happened yet.

Service dynamics can hurt!

Service dynamics are a huge hurdle for “new” developers

DI and IoC can turn even experienced brains inside out if they aren’t prepared. Thankfully, they do seem to recover.

DS helps a LOT

But …

Service dynamics can still hurt.

Being really lazy is hard work!

Easy to make assumptions

Service availability

Event ordering

Especially in our tests

Is the server started?

The server

Is the server started?What does this boundary even mean

in an extensible system?

The server

Care about the services

you care about

What’s the schema for the configuration?

Devolved configuration is great. But ..

Tolerating unrecognised elements is great when your config is correct.

It’s not so good when your config is wrong.

Aggregated documentation is good for users.

Aggregated documentation is (sort of) needed for tooling

We generate an xsd at build-time so tooling can validate user config

Is it worth it?

Is it worth it?OH YES.

Our server is GREAT.

Starts in 3s …

… which we never have to do anyway…

Starts in 3s …

… because it’s fully dynamic

Starts in 3s …

… because it’s fully dynamic

Concise, shareable configuration

Did it all turn out the way we expected?

A funny thing happened while we were developing for developers …

OSGi was designed for …

Small embedded system

… but turned out to be perfect for …

Liberty was designed for …

Developer-scale

… but turned out to be perfect for…

BIG scale

BlueMix server farm

BIG scale

BlueMix server farm

BIG scale

Lots of Liberty instances

Thank you!

Questions?

@holly_cummins www.wasdev.net

Thank you!

Questions?

Oh, and I have a book!

@holly_cummins www.wasdev.net

Backup

</cleanSlate>Of course, we didn’t really get a clean

slate.Application compatibility had to be

preserved. !

Configuration Admin We rolled our own (sorry)

Parse and merge user configuration and bundle-provided defaults

Resolve variables

Provide configuration to consumers as required by the spec (mostly)

pid/reference

unique, final, variable, etc.

http://www-01.ibm.com/support/knowledgecenter/was_beta_liberty/com.ibm.websphere.wlp.nd.multiplatform.doc/ae/rwlp_extensions_osgi_metatype.html

human readable: 1h30m converted to unit of used by developer tools to

help prompt for the right kind of path: file vs. url

pid/reference

type=“String”ibm:type=“password”

The value is a “SerializedProtectedString”,

which is not a String.

pid/reference

This is some crazy stuff.

ibm:type=“pid” ibm:reference=“specific.service.pid”

Allows nested configuration elements

to define service relationships

IsolationWe mean this in a good way.

Liberty runtime serves two masters:

Typical Application Server paradigm(apps strictly separated from runtime) — API

Platform extender paradigm(the “app” is the runtime) — SPI

Persistent problem:how to allow apps or extensions to use their own versions of libraries that don't conflict with the runtime!?

Private-package declarations pull in redundant classes

Split packages never end well

making everything better with osgi - a happy case study in building a really nice runtime - h...

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