This document discusses the declining relevance of traditional Java application servers. It argues that application servers are no longer needed as containers for multiple applications due to limitations in isolation. Modern applications are better suited as individual JAR files with their own custom infrastructure and standard monitoring and deployment tools rather than relying on application server-specific approaches. Frameworks like Spring Boot and Dropwizard provide an alternative to application servers by allowing applications to be self-contained deployable units without dependency on external application server infrastructure.

1. Java App
Servers are
Dead!
Eberhard Wolff
Freelancer
Head Technology Advisory Board adesso
http://ewolff.com

2. Eberhard Wolff - @ewolff
Code

3. Eberhard Wolff - @ewolff
2003

4. App Server =
Java EE or
Servlet
Container

5. Eberhard Wolff - @ewolff
An Application
on a server
needs an
Application Server!

6. Eberhard Wolff - @ewolff
Why??
The Price We Pay
What now?

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App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

8. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

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Multiple Applications
• Isolation
• ClassLoader
• Can lead to non-trivial problems
App Server
App 1 App 2 App 3 App 4

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Isolation
• ClassLoader is not enough
• CPU?
• Memory?
• Filesystems?
• Applications are not isolated
• Even individual parts are not isolated
• i.e. JMS might eat away resources
from web requests

11. Eberhard Wolff - @ewolff
Isolation is Impossible
• Operating systems isolate processes
from each other
• CPU, memory …
• Resource allocation: #1 feature for
operating systems
• Either the JVM becomes an
operating systems
• …or isolation won’t be perfect

12. Eberhard Wolff - @ewolff
Multiple Applications
• Is that really what happens?
• Java EE spec talks about
“components”
• not Apps
App Server
App 1 App 2 App 3 App 4

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One Application
App Server
App 1 App 2 App 3 App 4

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One Application
App Server
• Component e.g. WAR, EJB JAR …
• Different ClassLoader isolation
needed
• OSGi like
• Memory/CPU isolation still missing
Component 1 Component 2App

15. Eberhard Wolff - @ewolff
What It Is More Like…
App Server
App 1
App Server
App 1
App Server
App 1
App Server
App 1
App Server
App 1
App Server
App 1
Cluster

16. App Server:
container for
one
application

17. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

18. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

19. Eberhard Wolff - @ewolff
Infrastructure
• Two Phase Commit
• Net / Threads
• APIs

20. Eberhard Wolff - @ewolff
Infrastructure:
Two Phase Commit
• Idea: Coordinate multiple
transactional resources
• A talk in its own right
• 2 DBs: Consider a different
architecture
• DB + JMS: Tx Synchronization
might help
• http://bit.ly/JMS-2PC

21. Eberhard Wolff - @ewolff
Infrastructure:
Two Phase Commit
• Slows down the good case in favor
of the bad case
• No 100% - 2PC can fail
• Of limited use in distributed
systems
• E.g. REST + 2PC?
• NoSQL + 2PC?
• Limits scalability

22. Eberhard Wolff - @ewolff
Infrastructure: Net / Threads
• Support i.e. for HTTP and thread
pooling
• Connection pooling
• Can be done inside the application
• Embedded servers (Tomcat, Jetty)

23. Eberhard Wolff - @ewolff
Infrastructure: APIs
• EJB, CDI, JPA, JSF...
• Version tied to App Server version
• App depends on Application Server
• New APIs can’t be used until new
App Server in production
• Version conflicts might arise

24. Eberhard Wolff - @ewolff
Infrastructure: APIs
• Usually not every need covered
• …so additional libraries are used
• App Server APIs can be replaced by
libraries
• Makes application more portable

25. Eberhard Wolff - @ewolff
Infrastructure:
Application independent?
• Each application has its own
infrastructure
• E.g. database connections
• + specific configuration
• Might even add its own libraries to
the AppServer
• Big no-no if the App Server should
be application independent

26. Eberhard Wolff - @ewolff
Dependencies
App Server / Application
App Server
Application
Libraries
Infrastructure
Specific
configuration
Cyclic dependency
i.e. one component

27. Application
Servers
are just
another part of
the Application

28. Eberhard Wolff - @ewolff
You Don‘t Agree?
• Can you deploy your application on a
different server?
• On a different version of the same server?
• Without modifications to the server?
• Do you deploy other applications on the
App Server?
• Could you?
• Is the application server or an installation
script in your version control?

29. Eberhard Wolff - @ewolff
Application Server: Just One
Kind of Infrastructure
• App Server focus on interactive
(web) applications
• Other types of application:
• Batches
• Integration
• Map / Reduce
• App Servers are no universal
infrastructure

30. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

31. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

32. Eberhard Wolff - @ewolff
Deployment
• Deployment Format: WAR, EAR, JAR...
• No way to define dependencies outside
Application
• i.e. App Server version, database etc
• Operations usually work with deb, RPM…
• Completely different tool chain
• Also: Usually Unix services to start
applications

33. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

34. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... infrastructure
• …deployment
• …monitoring

35. Eberhard Wolff - @ewolff
Monitoring
• Provided by JMX
• Can be integrated in SMNP etc J
• New tools arise
• Logs + Logstash / Kibana or Splunk
• REST based monitoring resources
• Scripts for monitoring

36. App Server are
needed for
monitoring &
deployment

37. App Server
come with
their own
Ops Tool Set

38. Eberhard Wolff - @ewolff
App Server...
• …container for multiple applications
• ... provide infrastructure
• …support deployment
• …support monitoring
1 App per server ..or per cluster
App Server part of the application
Deployment & monitoring OK
but different tools

39. The Price
We Pay

40. Eberhard Wolff - @ewolff
Slower Turn Around
• Code
• Package a WAR
• Install it
• Have it unpacked
• Test
• Solutions: JRebel, Spring Loaded
• But: Why is it done at all??
Why??

41. Eberhard Wolff - @ewolff
App Server: Complex
Deployment
• Deployment: not just an application
• But also an Application Server
• App Server configuration more
complex than Application
configuration
• Look at automation scripts with
Puppet / Chef etc

42. Eberhard Wolff - @ewolff
Cyclic Dependency
Application – App Server
• Application and App Server must fit
each other
• Configuration must be compatible
• For each developer and each testing
stage
• Old configuration e.g. for bug fixes
• Hard to get right

43. Eberhard Wolff - @ewolff
Deployment Is Important
• Continuous Delivery means a lot
more deployment
• Must optimize deployment
Commit
Acceptance
Tests
Capacity
Tests
Explorative
Tests
Production
Many times per day

44. Eberhard Wolff - @ewolff
Continuous Delivery
• Applications deployed more
frequently
• …in many different stages
• Simple deployment even more
important
• App Servers become bigger headache

45. Continuous
Delivery increases
demand for
simple
infrastructure.

46. Eberhard Wolff - @ewolff
Different Ops Mindset
• App Server administrator?
• Deployment, monitoring etc. have
been solved already!
• Package manager
• Ops Monitoring
• Why not stick to general solutions?

47. Eberhard Wolff - @ewolff
DevOps
• DevOps and Continuous Delivery:
focus on “normal” tools and
approaches
• Dev will see more than only Java
Apps and App Servers
• Need different tools

48. Eberhard Wolff - @ewolff
Micro Services
• Build software composed of services
• Service has business meaning
• i.e. Order, Catalog etc
• Services (re)deployed
independently
• …instead of deployment monolith
• …and communicate e.g. via REST

49. Eberhard Wolff - @ewolff
Micro Services: eCommerce
Catalog
Order Processing
Customer
Recommendation

50. Install and
configure App
Server for each
Microservice??

51. Eberhard Wolff - @ewolff
Micro Services
• Service might have different non-functional
requirements
• So different infrastructure might be needed
• E.g. asynchronous applications
• Traditional Servlets
• Batches
• Map / reduce
• ….
• App Server just provide one kind of
infrastructure

52. Eberhard Wolff - @ewolff
The Price We Pay
App
Server
Slow Turn
Around
Standard
OPs Tools
Continuous
Delivery
Micro
Services
App Server specific
OPs tools
Deployment
complex
One infrastructure
doesn’t fit all
One App Server
per Micro Service?Smaller
deployment units

53. Eberhard Wolff - @ewolff
RIP Application Server!

54. What now??

55. Eberhard Wolff - @ewolff
The Re-Rise of the
Applications
• Create a JAR files
• …that contains a main class
• Custom infrastructure
• E.g. HTTP server
• Or Batch
• …

56. Eberhard Wolff - @ewolff
Monitoring & Deployment
• Rely on standard Ops deployment
and monitoring tools
• REST based monitoring URLs
• Evaluate log files

57. Eberhard Wolff - @ewolff
Application: Benefit
• Easier to Deploy: Just a JAR
• + command line
• + config file
• Debug & run in IDE
• Acceptance tests etc much easier
• Ensured: Infrastructure compatible
with application

58. Spring Boot
Actuator &
CRaSH Demo

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Deploy Demo
• mvn package
• Show java –jar with JAR

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Actuator Demo
• Open
http://localhost:8080/
monitor.html
• Show metrics / trace
• Show info and
application.properties

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Demo CRaSH
• ssh -p 2000 user@localhost
• Password in log output
• help
• Mention jpa / jdbc / problems
• thread top CTRL-C
• metrics
• dashboard

62. Eberhard Wolff - @ewolff
Technologies
• Spring Boot
• see my talk on Wednesday
• Dropwizard by Yammer
• Vert.x
• see Tim Fox’s talk this evening
• Play Framework

63. Eberhard Wolff - @ewolff
Thank You!!
eberhard.wolff@gmail.com
@ewolff