Kubernetes allows a lot. After discovering its features, it’s easy to think it can magically transform your application deployment process into a painless no-event. For Hello World applications, that is the case. Unfortunately, not many of us do deploy such applications day-to-day. You need to think about application backward compatibility, possible rollback, database schema migration, etc. I believe the later is one of the biggest pain point. In this talk, I’ll demo how to update a Spring Boot app deployed on a Kubernetes cluster with a non-trivial database schema migration with the help of Flyway, while keeping the service up during the entire update process.

1. @nicolas_frankel
Zero-downtime Deployment
With Kubernetes, Flyway and Spring Boot
Nicolas Fränkel

2. @nicolas_frankel
Me, myself and I
 Former developer, team lead, architect,
blah-blah
 Developer Advocate
 Curious about Kubernetes
 Loves the Spring framework

3. @nicolas_frankel
Hazelcast
HAZELCAST IMDG is an operational,
in-memory, distributed computing
platform that manages data using
in-memory storage and performs
execution for breakthrough
and scale.
HAZELCAST JET is the ultra
fast, application embeddable,
3rd generation stream
processing engine for low
latency batch and stream
processing.

4. @nicolas_frankel
Why zero-downtime?
1. Engineers want it
 It’s ”cool”
2. Users want it
 It’s expected
3. Business wants it
 It’s revenue

5. @nicolas_frankel
Blue-Green deployment

6. @nicolas_frankel
Blue-Green deployment

7. @nicolas_frankel
Blue-Green deployment variant

8. @nicolas_frankel
Issues with Blue-Green deployment
 Routing latency
 “Lagging” users
 Database management
• Migration
• Or compatibility

9. @nicolas_frankel
1.0 1.01.02.0 2.0 2.0
Rolling updates principle

10. @nicolas_frankel
Kubernetes to the rescue!
apiVersion: apps/v1
kind: Deployment
spec:
replicas: 3
strategy:
rollingUpdate:
maxSurge: 0
maxUnavailable: 1
type: RollingUpdate

11. @nicolas_frankel
Rolling update options
 maxSurge:
• Number of extra pods
 maxUnavalaible:
• Number of down pods allowed

15. @nicolas_frankel
Apps don’t start instantly
 Kubernetes need to know the
application’s state
• To mark the pod ready
 Spring Boot offers the actuator
• With the /health endpoint

16. @nicolas_frankel
Kubernetes-Spring Boot integration magic
spec:
containers:
- name: spring-boot-app
image: zerodowntime:1.0
readinessProbe:
httpGet:
path: /actuator/health
port: 8080

17. @nicolas_frankel
Most talks stop there...
 Let’s pat ourselves on the shoulder
 Hello world apps FTW!

18. @nicolas_frankel

19. @nicolas_frankel
It’s the database, stupid!
1.0 1.01.02.0
1.02.0

20. @nicolas_frankel
Version compatibility
Consecutive app versions must be
schema-compatible

21. @nicolas_frankel
It’s still the database...
1.0 1.01.02.0
1.0
2.0 2.0
2.0

22. @nicolas_frankel
Making changes for-/backward compatible
Break down a change into a serie of side-
by-side compatible changes

23. @nicolas_frankel
A sample use-case
Separating a single table into 2 tables with
a Primary Key - Foreign Key relation

24. @nicolas_frankel
Database schema migration

25. @nicolas_frankel
Steps decomposition
1. Create ADDRESS table
• App use the PERSON table data as previously
• Trigger copy data to ADDRESS table
2. The ADDRESS becomes the “source of truth”
• App now uses the ADDRESS table data
• Trigger copy data to the PERSON table
3. Stop copying the data
4. (Remove extra columns in the PERSON table)

26. @nicolas_frankel
Spring Boot specifics
 Disable automatic DDL creation/update
 Delegate to Flyway
• (Or Liquibase)

27. @nicolas_frankel
Flyway
 “Version control for your database.
 Robust schema evolution across all your
environments.
 With ease, pleasure and plain SQL.”
-- https://flywaydb.org/

28. @nicolas_frankel
Flyway 101
 Based on migrations
 A migration is a SQL script
 Each migration is versioned
 Flyway records migrations in a dedicated
table

29. @nicolas_frankel
Running the migration
 Flyway CLI
 Job
 initContainer
 Spring Boot integration
 etc.

30. @nicolas_frankel
Spring Boot Flyway integration
 Migrations are stored in the
db/migrations folder
 Automatically applied at application
startup

31. @nicolas_frankel

32. @nicolas_frankel
Takeaways
1.Zero-downtime is possible
2.It’s not free
3.It has an impact on how to
code/design/plan

33. @nicolas_frankel
Thanks for your attention!
 https://blog.frankel.ch/
 @nicolas_frankel
 https://hazelcast.org/
 https://bit.ly/0downtime