Deployment with a Version Control System such as Subversion or Git

Scope

• Version Control Systems are frequently used in software development. They can be applied as a basis for managed deployment of job-related objects, however, they are not focused on this purpose and therefore do not support specific deployment strategies. The basic functionality includes
  • to rollback to an older release if required.
  • to have changes documented.
  • to commit changes that are relevant for target environments.
  • to exclude test files and configuration files by not adding them to the repository.
• This article provides some considerations and recommendations on deployment strategies. Users will have to determine the applicability of the repspective deployment strategy on their own.
• SOS does not claim any preferences for a specific Version Control System product. At the time of writing no specific functionality is available that would make e.g. Git more useful for deployments than Subversion or Team Foundation Server. Therefore this article is not about comparing or recommending specific products, instead it will use Git and Subversion to explain the required repository operations for deployments.

Prerequisites

Requirements

• Deployments include to consistently deploy all job-related objects, i.e. Jobs, Job Chains, Orders, Process Classes, Locks etc., that are referenced by each other and that make up a release.
• Deployments consider configuration items, e.g. path names, ports, folders, that are applicable to all environments and configuration items that are specific for an individual environment.
• Deployments can be carried out for a number of environments. Some users might use development, integration and production environments, other users might add sandbox or user acceptance test environments.
• Deployments are caried out for releases, not for changes of individual files. Version control is not a replacement for creating backups of your job environments.
• Capability to rollback to a previous release: Should a problem be detected e.g. in a production environment and not enough time be available for thorough analysis, then the option is to rollback immediately to a consistent previous state of job-related objects.

Environments

• Three environments are required for managed deployments:
  • Development
    • Modifications to job-related objects are carried out in this environment.
  • Integration
    • No modifications are applied to job-related objects.
    • Configuration items are specific for this environment.
  • Production
    • No modifications are applied to job-related objects.
    • Configuration items are specific for this environment.
• The purpose of the integration environment is to carry out tests of deployed objects. This includes testing the completeness, interoperability and accuracy of deployed objects. 
• Should users want to skip the use of an integration environment then tests would have to be performed in a production environment which is not a recommended strategy.

Terms used with Version Control Systems

• Repository
  • Repositories are logical units in a Version Control System to store Branches of objects that can be assigned permissions for access by different users and groups.
• Working Copy
  • Working Copies are local copies of files from a Repository. Modifications are applied to files in a Working Copy that later on can be Comitted to the Repository.
• Branch
  • A Branch corresponds to the current status of the job-related objects that have been added to the Repository by Commit operations.
  • Only one Branch at a time should be used for job deployment. Multiple branches are frequently used to organize the contributions of a number of developers who work in parallel on the same sources. It is not a recommended scenario for job development to have multiple engineers work in parallel on the same jobs.
  • Branches can be tagged, e.g. assigned a Release number.
• Commit
  • Commits include to submit a fully functional and deployable copy of job-related objects from a Working Copy to a Repository.
  • Commits are not intended for backup of Working Copies for job-related objects.
• Release
  • Releases are tagged Branches that are not modified after deployment.
  • Release numbers can be applied according to individual conventions. Semantic Versioning is a frequently used standard for release numbering (Major.Minor.Patch).

Use Cases

• Initial creation of a repository with the configuration items of a JobScheduler instance.
  • Configuration items are stored in the live folder.
  • These items should become part of the repository.
  • The live folder should be a checked out version of the configuration.
• Initial Deployment
  • Initially deploy a release to an integration or production environment.
• Update Management
  • Deploy a maintenance release to an existing environments.
  • Existing job-related objects will be replaced. 
  • Dropped job-related objects will be removed.
  • Existing configuration items should be considered and maintained.

• Rollback to a previous release

  1. Identify the release to which you want to fall back.
  2. With Subversion/Git operations get the files of the desired release.
  3. Deploy the desired release as stated with the "Update Management"

Best Practices

Separating configuration items specific for an environment

• When carrying out the deployments it is possible that parameter values are not applicable to target environments, e.g. the names of files, folders, printers etc.
• In a first step users should clearly separate all configuration items that are specific for an environment from job-related objects and configuration items that can be applied to all environments without changes.

• Examples for configuration items that should be considered include

  • host names for process classes
    • Solution: Having a set of process classes in each environment that will not be part of the deployment procedure. This configuration will be handled directly in the specific environment.
  • directories for file order sources
    • Solution: Having different file order sources in each environment that will not be part of the deployment procedure. This configuration will be handled directly in the respective environment.
  • values for parameters, e.g. database connection strings
    • Solution: Make use of include files.
    • Solution: Make use of environment variables that will be substituted at run time.

Use of Environment Variables

• Use environment variables that accept different values in target environments for
  • File Order Sources
  • Directories in file names
     

<job_chain>
   <file_order_source directory="${file_input_dir}\input" regex=".*"/>
   ...
</job_chain>

Use of Include Files for Parameters

Use include files to specify parameter values:

<order>
	<params>
		<include live_file="myorder.params.xml" node=""/>
    </params>
    ...
</order>

where the file myorder.params.xml could look like this:

<params >
	<param name="par1" value="value1"/>
	<param name="par2" value="value2"/>
    ...
</params>

Use of Include Files for Scripts

Use different script include files for development, integration and production environments:

<job order="yes">
	<script language="shell">
		<include live_file="include_scriptfile.sh"/>
	</script>
    <run_time />
</job>

Example for the Handling of different Include Files for Parameters and Scripts

• create a folder include_files (located parallely to the live folder)
• create sub-folders for target environments, e.g. dev, int and prod.
• create the same sub-folders for all target environments as in the development environment live folder
• create the include files in the sub-folders for the target environments
• create a folder in the repository that contains the folder include_file
• create a working copy with the import, delete and checkout commands (see below).
• When committing the include_files folder you should also commit the live folder (and vice versa) to guarantee consistency between both folders.
• When deploying to the integration environment then  export the include_files/int folder to the target live folder.
• When deploying to the production environment then export the include_files/prod folder to the target live folder.

As you have a working copy in the live folder for dev, the include files from dev will be deployed when exporting the dev folder. But with the second export from the include_files folder, the dev files will be overwritten with the correct version. An alternative approach is that also the live folder in dev is not a working copy but will be updated with an export command from the dev working copy.

Handling of Version Control Systems

• Discipline
  • Due to the possible sharing of tasks between job development and integration testing a test manager might not know exactly what files are included with the delivery of a release, i.e. he or she cannot check the completeness of deployed objects.
  • Therefore the discipline of the job developer to commit complete and accurate jobs and job dependencies is vital to the deployment process.
• Quality of the development environment
  

  • When managing test configuration files in the development environment you should take care not to commit them to the repository. To achieve this, do not add such files to the repository. Typically you can add such files to an ignore list (available with Git and Subversion). You should take into account that each configuration item that has been committed to the repository will be deployed to the integration or production environments some time later.

Deployment

Deployment Process Flow

Explanations

The deployments from development to integration and production environments make use of the following steps:

• Development Environment:
  • add the job files and configuration files to the repository.
  • do not add files to the repository that are used exclusively for testing in this environment, e.g. mock files.
• Integration Environment
  1. Update a local working copy from the development branch of the repository. Do not use the live folder directly but a separate folder outside of the JobScheduler installation for updating.
  2. Manage configuration files for this environment in a separate folder and add them to the integration branch of the repository.
  3. Update the integration environment, i.e. the live folder, first from the working copy for the development branch 1) and then from the working copy for configuration files from the integration branch 2).
• Production Environment
  • Apply the same local working copies and deployment steps as for the integration environment.

Deployment Operations with Subversion and Git

The following table describes the deployment operations with Subversion and Git.