Making everything better with OSGi - a happy case study in building a really nice runtime - H Cummins

Making everything better
©2014 IBM Corporation
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 production.
For development, historically not so well-suited.

History

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

around since 1998
History
forever

around since 1998
Big codebase
History
forever

History
around since 1998
forever
Big codebase
Big customer base

History
around since 1998
forever
Big codebase
Big customer base
Big workloads

History
around since 1998
forever
Big codebase
Big customer base
Big workloads
… Big inhibitors to massive change

History
around since 1998
This is not a
complaint.
Big codebase
Big customer base
Big workloads
This is a problem we are
happy to have.
forever

History
around since 1998
This is not a
complaint.
Big codebase
Big customer base
Big workloads
This is a problem we are
happy to have.
But it is still a
problem.
forever

Code that has been around
forever…

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

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

forever…
?!
and is used enough,

forever…
and is used enough,
dragons
?!

forever…
and is used enough,
dragons
?!
Especially code that has
roots
going back to late ‘90s…

How do you manage dragons?
By Steve Collis from Melbourne,
Australia [CC-BY-2.0 (http://
creativecommons.org/licenses/
by/2.0)], via Wikimedia Commons

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?

Did that fix everything?
Not quite.
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?

What if…
Developer-friendly

What if…
Developer-friendly
Simple

What if…
Developer-friendly
Simple
Dynamic

What if…
Developer-friendly
Simple
Dynamic
Light-weight

What if…
Developer-friendly
Simple
Dynamic
Light-weight
Composable / Flexible

What if…
Developer-friendly
Simple
Dynamic
Light-weight
Extensible

What if…
Developer-friendly
Simple
Dynamic
Light-weight
Extensible
human usable
configuration
selectable content
clear API/SPI
runtime/app
isolation

runtime
only
some combination of
technologies
!
app-centered
everything
What if…
grokable
config
provisioning

What if…
grokable
config
runtime
only
provisioning
some combination of
technologies
!
app-centered
everything
How do we do this?

What if…
runtime
only
some combination of
technologies
!
everything app-centered
And yet allow this?
no restarts

What if…
And for crying out loud,
can we prevent THIS?!
3rd runtime
party
bundle
B
system
bundle
A

What if…
Applicati
on
3rd runtime
party
bundle
B
system
bundle
A

What if…
Applicati
on
X
3rd runtime
party
bundle
B
system
bundle
A

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 model
Level 1: Ad Hoc

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules
Level 3: Modularity

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules
Level 3: Modularity
Level 4: Loose coupling

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules
Level 3: Modularity
Level 5: Devolution

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules
Level 3: Modularity
Level 5: Devolution
Level 6: Dynamism

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules
Level 3: Modularity
Level 5: Devolution
Level 6: Dynamism
Level 7: Peter Kriens

OSGi maturity model
Level 1: Ad Hoc
Level 2: Modules
Level 3: Modularity
Level 5: Devolution
Level 6: Dynamism
Websphere Full Profile

OSGi maturity model
Level 1: Ad Hoc
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

Configuration
Settled on XML for configuration format
Ubiquitous
Expressive
BUT, for simplicity:
single file
usable defaults
<server description=“simple”>
<featureManager>
<feature>jsp-2.2</feature>
</featureManager>
!
<httpEndpoint id=“defaultHttpEndpoint”
httpPort=“9080” httpsPort=“9443” />
</server>

Configuration
Composable system requires composable
configuration:
Individual components own their config
No centralized repository
No externally defined global config model

Configuration
configuration:
Configuration Admin and Metatype
- job done

Configuration
configuration:
Configuration 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

Metatype
Define configuration everywhere human else.
readable:
and constraints in one place, it gets used
1h30m converted to unit of
choice
pid/reference

Metatype
readable:
choice
used by developer tools to help
prompt for the right kind of
path: file vs. url
pid/reference

Metatype
readable:
choice
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.

Using OSGi Services…
?
Declarative Blueprint
Services
yes, there are others.
We focused on these two.

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

Who in their right mind wants to manage
OSGi services themselves??
Exactly. NOBODY.
?
Services

Declarative Services
We 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
THIS
Application
X
3rd runtime
party
bundle
B system
bundle
A

Package privacy

Package privacy
OSGi lets you keep your internals private.

Package privacy
Your externals are public.

Package privacy
Your externals are public.
Private Public

Granularity
bundle C
bundle A
bundle B

Granularity bundle D
bundle E
bundle F
bundle G
bundle H
bundle M
bundle N
bundle I
bundle K
bundle L bundle M
bundle O bundle J bundle P
bundle N
bundle Q
bundle C
bundle A
bundle B

bundle E
bundle F
bundle G
bundle H
bundle M
bundle N
bundle I
bundle K
bundle L bundle M
bundle N
bundle Q
bundle C
bundle A
bundle B
Wait a minute, it wasn’t
supposed to be that
public …

bundle E
bundle F
bundle G
bundle H
bundle M
bundle N
bundle I
bundle K
bundle L bundle M
bundle N
bundle Q
bundle C
bundle B bundle A

Granularity
bundle D
bundle F
bundle E
bun dle G
b undle M
bundle N
bundle I
bundle K
bundle J
bundle O
bundle P
bundle N
bundle L
bundle M
Q
bundle C
bundle A
bundle B

Granularity
bundle D
bundle F
bundle E
bun dle G
b undle M
bundle N
bundle I
bundle K
bundle J
bundle O
bundle P
bundle N
bundle L
bundle M
Q
bundle C
bundle A
bundle B
What bundles do I
actually need?

Granularity
bundle D
bundle F
bundle E
bun dle G
b undle M
bundle N
bundle I
bundle K
bundle J
bundle O
bundle P
bundle N
bundle L
bundle M
Q
bundle C
bundle A
bundle B
What bundles do I
actually need?
Could I just have an archive,
please?

This is not a new requirement

Lots of attempts to solve this problem

Eclipse features

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

Granularity
Package isolation

Granularity
Package isolation
Packaging

bundle E
When better boxes is not
bundle D enough
bundle F
bundle G
bundle H
bundle M
bundle N
bundle I
bundle K
bundle L bundle M
bundle N
bundle Q
bundle C
bundle A
bundle B

bundle E
bundle D enough
bundle F
bundle G
bundle H
bundle M
bundle N
bundle I
bundle K
bundle L bundle M
bundle N
bundle Q
bundle C
bundle A
bundle B
Extension

bundle E
bundle D enough
bundle F
bundle G
bundle H
bundle M
bundle N
bundle I
bundle K
bundle L bundle M
bundle N
bundle Q
bundle C
bundle A
bundle B
Resolver
hook
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

Provisioning
Dynamically install features (subsystems) based on
configuration

Provisioning
configuration
Adding or removing features …

Provisioning
configuration
installs or uninstalls bundles…

Provisioning
configuration
which adds or removes configurations…

Provisioning
configuration
which triggers the creation or removal of services!

Provisioning
configuration
No restart needed.
!
#really
which triggers the creation or removal of services!

Did we get rid of
all the dragons?

Did we get rid of
all the dragons?
By Abraham (Own work) CC-BY-3.0 via Wikimedia Commons

Did we get rid of
all the dragons?
The OSGi
dragon
By Abraham (Own work) CC-BY-3.0 via Wikimedia Commons

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

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 ?

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

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

developers
DS helps a LOT

developers
DS helps a LOT
But …

Service dynamics can still hurt.

Being really lazy is hard work!

Easy to make assumptions

Service availability

Event ordering

Event ordering
Especially in our tests

Is the server started?

Is the server started?
The server

Is the server started? What does this
boundary even mean
in an extensible
system?
The server

Is the server started? What does this
boundary even mean
in an extensible
system?
Care about
the services
you care
about

What’s the schema for the
configuration?

configuration?
Devolved configuration is great. But ..

configuration?
Tolerating unrecognised elements is great when your config is correct.

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

configuration?
Aggregated documentation is good for users.

configuration?
Aggregated documentation is (sort of) needed for tooling

configuration?
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.

Is it worth it?
OH YES.
Our server is GREAT.

Is it worth it?
OH YES.
Starts in 3s …

Is it worth it?
OH YES.
Starts in 3s …
… which we never have to do anyway…

Is it worth it?
OH YES.
Starts in 3s …
… because it’s fully dynamic

Is it worth it?
OH YES.
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 …

OSGi was designed for …
Small embedded system

… but turned out to be perfect for …

Liberty was designed for …

Liberty was designed for …
Developer-scale

… but turned out to be perfect
for…

for…
BIG scale

BlueMix server
farm
for…
BIG scale

BlueMix server
farm
for…
BIG scale
Lots of Liberty
instances

Thank you!
Questions?
@holly_cummins
www.wasdev.net

Thank you!
Questions?
@holly_cummins
www.wasdev.net
Oh, a n d I h ave a b o o k !

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)

Metatype
human readable:
Define configuration and constraints in one place, it gets used everywhere else.
1h30m converted to unit of used by developer tools to
help prompt for the right
kind of path: file vs. url
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

Metatype
type=“String”
ibm:type=“password”
The value is a “SerializedProtectedString”,
which is not a String.
pid/reference

Metatype
This is some crazy stuff.
ibm:type=“pid”
ibm:reference=“specific.service.pid”
Allows nested configuration elements
pid/reference
to define service relationships

Isolation
We 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 Cummins

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