Deploying multiple apps with different versions using a single Ansible command

Problem description

In this article, we will look at how to deal with the following scenario. Our system consists of several applications. Let’s imagine we need to deploy some (or all) of those apps with a single command. We also need to specify a common version for all apps or different versions for each app. The desired command could look like this:

ansible-playbook -i prod app-1.yml app-2.yml app-3.yml -e app_1_version=1.2.3 -e app_version=3.2.1

Such a command should result in the installation of app1 in version
1.2.3 and remaining apps in version 3.2.1.

The main difficulty here is that we use the same tasks (e.g. common role) for deploying all apps, so the app version variable is dynamic. Additionally, our app names can contain dashes (which is an invalid character in variable names) so we need to replace it with an underscore.

How to get a dynamic variable

First things first. We need to have access to all variables if the names of those variables are dynamic. Variables must be passed in a form that allows us to retrieve their value using a dynamic variable name. This is where a vars variable comes to the rescue.

vars is a special variable in the form of a dictionary, where we can get a specific value using the syntax of vars[key]. Now, if we have our app name in a variable app_name we can get that variable using the syntax vars[app_name | replace('-', '_') + '_version']. Alternative syntax for this is lookup('vars', app_name | replace('-', '_') + '_version'), but the first one is more pleasant to us. Anyway, not bad, is it?

Default app version

Here comes our additional requirement – a default app version. That’s
a piece of cake – we just have to check if a variable is defined and
take the default version, right? Both solutions above come with some
default support.

vars[spring_app_name | replace('-', '_') + '_version'] | default(app_version) }}
lookup('vars', spring_app_name | replace('-', '_') + '_version', default = app_version)

All we need to do now is to register it in a fact (like
target_app_version) and we are good to go. This is not very
readable though, with all those braces and filters. Can we do it
better?

Custom filter plugin

We can create our custom filter plugin. Let’s see the usage first and focus on the implementation afterwards. In order to get the app version using a custom filter, we can use
something like this:

app_name | ver(vars)

To create a filter, we must add it in the folder filter_plugins of our role. Filters are written in python, so let’s add the following content to ROLE_NAME/filter_plugins/ver.py:

class FilterModule(object):
    def filters(self):
        return {
            'ver': self.ver
        }

    @staticmethod
    def ver(app_name, vars):
        app_name_version = app_name.replace('-', '_') + '_version'
        if app_name_version in vars:
            return vars[app_name_version]
        elif 'app_version' in vars:
            return vars['app_version']
        else:
            raise Exception('No ' + app_name_version + ' or app_version defined')

This solution also has an additional advantage – it raises a meaningful and descriptive error, which is much better than in previous solutions.

Summary

What we achieved is the ability to retrieve the app version from the command line parameter even if multiple apps were deployed at once. Additionally, we are able to specify the default version if a specific version for the app is not defined. Finally, we simplified playbooks code by moving complicated formulas to a custom plugin, providing a descriptive error as well.

You May Also Like

How to automate tests with Groovy 2.0, Spock and Gradle

This is the launch of the 1st blog in my life, so cheers and have a nice reading!

y u no test?

Couple of years ago I wasn't a big fan of unit testing. It was obvious to me that well prepared unit tests are crucial though. I didn't known why exactly crucial yet then. I just felt they are important. My disliking to write automation tests was mostly related to the effort necessary to prepare them. Also a spaghetti code was easily spotted in test sources.

Some goodies at hand

Now I know! Test are crucial to get a better design and a confidence. Confidence to improve without a hesitation. Moreover, now I have the tool to make test automation easy as Sunday morning... I'm talking about the Spock Framework. If you got here probably already know what the Spock is, so I won't introduce it. Enough to say that Spock is an awesome unit testing tool which, thanks to Groovy AST Transformation, simplifies creation of tests greatly.

An obstacle

The point is, since a new major version of Groovy has been released (2.0), there is no matching version of Spock available yet.

What now?

Well, in a matter of fact there is such a version. It's still under development though. It can be obtained from this Maven repository. We can of course use the Maven to build a project and run tests. But why not to go even more "groovy" way? XML is not for humans, is it? Lets use Gradle.

The build file

Update: at the end of the post is updated version of the build file.
apply plugin: 'groovy'
apply plugin: 'idea'

def langLevel = 1.7

sourceCompatibility = langLevel
targetCompatibility = langLevel

group = 'com.tamashumi.example.testwithspock'
version = '0.1'

repositories {
mavenLocal()
mavenCentral()
maven { url 'http://oss.sonatype.org/content/repositories/snapshots/' }
}

dependencies {
groovy 'org.codehaus.groovy:groovy-all:2.0.1'
testCompile 'org.spockframework:spock-core:0.7-groovy-2.0-SNAPSHOT'
}

idea {
project {
jdkName = langLevel
languageLevel = langLevel
}
}
As you can see the build.gradle file is almost self-explanatory. Groovy plugin is applied to compile groovy code. It needs groovy-all.jar - declared in version 2.0 at dependencies block just next to Spock in version 0.7. What's most important, mentioned Maven repository URL is added at repositories block.

Project structure and execution

Gradle's default project directory structure is similar to Maven's one. Unfortunately there is no 'create project' task and you have to create it by hand. It's not a big obstacle though. The structure you will create will more or less look as follows:
<project root>

├── build.gradle
└── src
├── main
│ ├── groovy
└── test
└── groovy
To build a project now you can type command gradle build or gradle test to only run tests.

How about Java?

You can test native Java code with Spock. Just add src/main/java directory and a following line to the build.gradle:
apply plugin: 'java'
This way if you don't want or just can't deploy Groovy compiled stuff into your production JVM for any reason, still whole goodness of testing with Spock and Groovy is at your hand.

A silly-simple example

Just to show that it works, here you go with a basic example.

Java simple example class:

public class SimpleJavaClass {

public int sumAll(int... args) {

int sum = 0;

for (int arg : args){
sum += arg;
}

return sum;
}
}

Groovy simple example class:

class SimpleGroovyClass {

String concatenateAll(char separator, String... args) {

args.join(separator as String)
}
}

The test, uhm... I mean the Specification:

class JustASpecification extends Specification {

@Unroll('Sums integers #integers into: #expectedResult')
def "Can sum different amount of integers"() {

given:
def instance = new SimpleJavaClass()

when:
def result = instance.sumAll(* integers)

then:
result == expectedResult

where:
expectedResult | integers
11 | [3, 3, 5]
8 | [3, 5]
254 | [2, 4, 8, 16, 32, 64, 128]
22 | [7, 5, 6, 2, 2]
}

@Unroll('Concatenates strings #strings with separator "#separator" into: #expectedResult')
def "Can concatenate different amount of integers with a specified separator"() {

given:
def instance = new SimpleGroovyClass()

when:
def result = instance.concatenateAll(separator, * strings)

then:
result == expectedResult

where:
expectedResult | separator | strings
'Whasup dude?' | ' ' as char | ['Whasup', 'dude?']
'2012/09/15' | '/' as char | ['2012', '09', '15']
'nice-to-meet-you' | '-' as char | ['nice', 'to', 'meet', 'you']
}
}
To run tests with Gradle simply execute command gradle test. Test reports can be found at <project root>/build/reports/tests/index.html and look kind a like this.


Please note that, thanks to @Unroll annotation, test is executed once per each parameters row in the 'table' at specification's where: block. This isn't a Java label, but a AST transformation magic.

IDE integration

Gradle's plugin for Iintellij Idea

I've added also Intellij Idea plugin for IDE project generation and some configuration for it (IDE's JDK name). To generate Idea's project files just run command: gradle idea There are available Eclipse and Netbeans plugins too, however I haven't tested them. Idea's one works well.

Intellij Idea's plugins for Gradle

Idea itself has a light Gradle support built-in on its own. To not get confused: Gradle has plugin for Idea and Idea has plugin for Gradle. To get even more 'pluginated', there is also JetGradle plugin within Idea. However I haven't found good reason for it's existence - well, maybe excluding one. It shows dependency tree. There is a bug though - JetGradle work's fine only for lang level 1.6. Strangely all the plugins together do not conflict each other. They even give complementary, quite useful tool set.

Running tests under IDE

Jest to add something sweet this is how Specification looks when run with jUnit  runner under Intellij Idea (right mouse button on JustASpecification class or whole folder of specification extending classes and select "Run ...". You'll see a nice view like this.

Building web application

If you need to build Java web application and bundle it as war archive just add plugin by typing the line
apply plugin: 'war'
in the build.gradle file and create a directory src/main/webapp.

Want to know more?

If you haven't heard about Spock or Gradle before or just curious, check the following links:

What next?

The last thing left is to write the real production code you are about to test. No matter will it be Groovy or Java, I leave this to your need and invention. Of course, you are welcome to post a comments here. I'll answer or even write some more posts about the subject.

Important update

Spock version 0.7 has been released, so the above build file doesn't work anymore. It's easy to fix it though. Just remove last dash and a word SNAPSHOT from Spock dependency declaration. Other important thing is that now spock-core depends on groovy-all-2.0.5, so to avoid dependency conflict groovy dependency should be changed from version 2.0.1 to 2.0.5.
Besides oss.sonata.org snapshots maven repository can be removed. No obstacles any more and the build file now looks as follows:
apply plugin: 'groovy'
apply plugin: 'idea'

def langLevel = 1.7

sourceCompatibility = langLevel
targetCompatibility = langLevel

group = 'com.tamashumi.example.testwithspock'
version = '0.1'

repositories {
mavenLocal()
mavenCentral()
}

dependencies {
groovy 'org.codehaus.groovy:groovy-all:2.0.5'
testCompile 'org.spockframework:spock-core:0.7-groovy-2.0'
}

idea {
project {
jdkName = langLevel
languageLevel = langLevel
}
}