Initial commit

.gitignore

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+*~
+#*
+*#
+.#*
+.classpath
+.project
+.settings/
+.springBeans
+target/
+_site/
+.idea
+*.iml
+*.swp
+.factorypath
+*.logtjmeter
+.checkstyle
+.DS_Store
+*.log
+/spring-cloud-sleuth-core/nb-configuration.xml
+/spring-cloud-sleuth-core/nbactions.xml

README.adoc

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+= Database Update
+
+How to write the code of your app to allow doing A/B testing or/and continuous deployment.
+
+== Assumptions
+
+In order for the process to be relatively simple the following assumptions need to take place
+while developing the app:
+
+- use a database versioning tool (we'll be using https://flywaydb.org[Flyway])
+- the database changes need to be backwards compatible
+- if you want to do a backwards incompatible change you have to do it in a couple of deployments
+- we don't want to do DB rollbacks. Not doing them simplifies the deployment process (some rollbacks are close to impossible like rolling back a delete)
+- we want to ALWAYS be able to rollback the application one version back (not more)
+
+== The issue
+
+For readability we're versioning the apps with major increments.
+
+Why is this problem worth discussing? Doing A/B testing with Cloud Foundry is extremely simple - it's a matter of executing a single command. However it's not that trivial in terms of the application and the db.
+
+Let's take a look at the following example if you want to change the column name:
+
+WARNING: The following example is deliberately done in such a way that it will break. We're showing it to depict the problem of database compatibility.
+
+=== Changing the column name in backwards-incompatible way
+
+Let's assume that we have the DB in version `v1`. It has the column with a name `last_name`. We want to change it to `surname.` We have the app in version `1.0.0` which uses the `last_name` column in the code.
+
+==== Rolling a new backwards-incompatible version
+
+. in Flyway we're writing a script to change the column name from `last_name` to `surname`
+. we're writing our code to use the new `surname` column
+
+==== A/B testing
+
+The current situation is that we have an app deployed to production in version `1.0.0` and db in `v1`. We want to deploy the second instance of the app that will be in version `2.0.0` and update the db to `v2`.
+
+Steps:
+
+. a new instance is deployed in version `2.0.0` that updates the db to `v2`
+. in `v2` of the database the column `last_name` is no longer existing - it got changed to `surname`
+. the db and app upgrade is successful and you have some instances working in `1.0.0`, others in `2.0.0`. All are talking to db in `v2`
+. all instances of version `1.0.0` will start producing exceptions cause they will try to insert data to `last_name` column which is no longer there
+. all instances of version `2.0.0` will work without any issues
+
+As you can if we do backwards incompatible changes of the DB and the application, A/B testing is impossible.
+
+==== Rolling back the application
+
+Let's assume that after trying to do A/B deployment we've decided that we need to rollback the app back to version `1.0.0`. We assumed that we don't want to roll back the database.
+
+Steps:
+
+. we shut down the instance that was running with version `2.0.0`
+. the database is still in `v2`
+. since version `1.0.0` doesn't understand what `surname` column is it will produce exceptions
+. hell broke loose and we can't go back
+
+As you can if we do backwards incompatible changes of the DB and the application, we can't roll back to a previous version.
+
+== Proper database update flow
+
+INFO: Here we'll present a more sound approach to deployment
+
+=== Adding a new column
+
+This situation is quite simple. Let's assume that we have the DB in version `v1`. It doesn't have the column `surname`.
+We also have the app in version `1.0.0` which doesn't use the `surname` column.
+
+==== Rolling a new version
+
+Steps:
+
+. migrate your db to create the new column called `surname`. Now your db is in `v2`
+. write the code to use the new column. Now your app is in version `2.0.0`
+
+If you're using Spring Boot Flyway those two steps will be performed upon booting the version `2.0.0` of the app.  If you're running database versioning tool manually then you'd have to do it in separate processes (first manually upgrade the db version and then deploy the new app).
+
+==== A/B testing
+
+The current situation is that we have an app deployed to production in version `1.0.0` and db in `v1`. We want to deploy the second instance of the app that will be in version `2.0.0` and update the db to `v2`.
+
+Steps:
+
+. a new instance is deployed in version `2.0.0` that updates the db to `v2`
+. in the meantime some requests got processed by instances being in version `1.0.0`
+. the upgrade is successful and you have some instances working in `1.0.0`, others in `2.0.0`. All are talking to db in `v2`
+. version `1.0.0` is not using the database's column `surname` and version `2.0.0` is. They don't interfere each other, no exceptions should be thrown.
+
+==== Rolling back the application
+
+The current situation is that we have app in version `2.0.0` and db in `v2`.
+
+Steps:
+
+. roll back your app to version `1.0.0`.
+. version `1.0.0` is not using the database's column `surname` thus rollback should be successful
+
+== Projects
+
+We will focus on the most interesting case of changing the column name. That change is backwards
+incompatible but we'll try to write it in such a way that A/B testing is possible.
+
+[source,bash]
+-------
+├── boot-flyway-v1        - 1.0.0 version of the app with v1 of the schema
+├── boot-flyway-v2        - 2.0.0 version of the app with v2 of the schema (backwards-compatible - app can be rolled back)
+├── boot-flyway-v2-bad    - 2.0.0 version of the app with v2 of the schema (backwards-incompatible - app can't be rolled back)
+└── boot-flyway-v3        - 3.0.0. version of the app with v3 of the schema (app can be rolled back)
+-------

boot-flyway-v1/README.adoc

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+== Spring Boot Flyway Sample
+
+This sample demonstrates the flyway auto-configuration support.
+
+You can look at `http://localhost:8080/flyway` to review the list of scripts.
+
+This sample also enables the H2 console (at `http://localhost:8080/h2-console`)
+so that you can review the state of the database (the default jdbc url is
+`jdbc:h2:mem:testdb`).

boot-flyway-v1/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<!-- Your own application should inherit from spring-boot-starter-parent -->
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-parent</artifactId>
+		<version>1.3.3.RELEASE</version>
+	</parent>
+	<artifactId>spring-boot-sample-flyway</artifactId>
+	<name>Spring Boot Flyway Sample</name>
+	<description>Spring Boot Flyway Sample</description>
+	<url>http://projects.spring.io/spring-boot/</url>
+	<organization>
+		<name>Pivotal Software, Inc.</name>
+		<url>http://www.spring.io</url>
+	</organization>
+	<properties>
+		<main.basedir>${basedir}/../..</main.basedir>
+	</properties>
+	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-data-jpa</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-web</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-actuator</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.flywaydb</groupId>
+			<artifactId>flyway-core</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+			<scope>runtime</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-test</artifactId>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-maven-plugin</artifactId>
+			</plugin>
+		</plugins>
+	</build>
+</project>

boot-flyway-v1/src/main/java/sample/flyway/Person.java

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+/*
+ * Copyright 2012-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample.flyway;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+
+@Entity
+public class Person {
+	@Id
+	@GeneratedValue
+	private Long id;
+	private String firstName;
+	private String lastName;
+
+	public String getFirstName() {
+		return this.firstName;
+	}
+
+	public void setFirstName(String firstName) {
+		this.firstName = firstName;
+	}
+
+	public String getLastName() {
+		return this.lastName;
+	}
+
+	public void setLastName(String lastname) {
+		this.lastName = lastname;
+	}
+
+	@Override
+	public String toString() {
+		return "Person [firstName=" + this.firstName + ", lastName=" + this.lastName
+				+ "]";
+	}
+}

boot-flyway-v1/src/main/java/sample/flyway/PersonRepository.java

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+/*
+ * Copyright 2012-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample.flyway;
+
+import org.springframework.data.repository.CrudRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface PersonRepository extends CrudRepository<Person, Long> {
+
+}

boot-flyway-v1/src/main/java/sample/flyway/SampleFlywayApplication.java

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+/*
+ * Copyright 2012-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample.flyway;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SampleFlywayApplication implements CommandLineRunner {
+
+	@Autowired
+	private PersonRepository repository;
+
+	@Override
+	public void run(String... args) throws Exception {
+		System.err.println(this.repository.findAll());
+	}
+
+	public static void main(String[] args) throws Exception {
+		SpringApplication.run(SampleFlywayApplication.class, args);
+	}
+
+}

boot-flyway-v1/src/main/resources/application.properties

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+spring.jpa.hibernate.ddl-auto=validate
+
+spring.h2.console.enabled=true

boot-flyway-v1/src/main/resources/db/migration/V1__init.sql

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+CREATE TABLE PERSON (
+	id BIGINT GENERATED BY DEFAULT AS IDENTITY,
+	first_name varchar(255) not null,
+	last_name varchar(255) not null
+);
+
+insert into PERSON (first_name, last_name) values ('Dave', 'Syer');

boot-flyway-v1/src/test/java/sample/flyway/SampleFlywayApplicationTests.java

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+/*
+ * Copyright 2012-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample.flyway;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration(SampleFlywayApplication.class)
+public class SampleFlywayApplicationTests {
+
+	@Autowired
+	private JdbcTemplate template;
+
+	@Test
+	public void testDefaultSettings() throws Exception {
+		assertEquals(new Integer(1), this.template
+				.queryForObject("SELECT COUNT(*) from PERSON", Integer.class));
+	}
+
+}

boot-flyway-v2-bad/README.adoc

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+== Spring Boot Flyway Sample
+
+This sample demonstrates the flyway auto-configuration support.
+
+You can look at `http://localhost:8080/flyway` to review the list of scripts.
+
+This sample also enables the H2 console (at `http://localhost:8080/h2-console`)
+so that you can review the state of the database (the default jdbc url is
+`jdbc:h2:mem:testdb`).