Advanced Provisioning and Orchestration with Infrastructure as Code (IaC)

In today’s increasingly complex cloud environments, Infrastructure as Code (IaC) has evolved from simple configuration scripts to sophisticated orchestration solutions capable of managing complex workflows and dependencies. Advanced orchestration in IaC, especially when using tools like SaltStack, can handle the provisioning, configuration, and deployment of multi-tier applications while ensuring that dependencies are met across multiple tiers, services, and servers.

In this article, we’ll explore advanced orchestration concepts in IaC, such as state management, dependency handling, and workflows. We’ll also guide you through a practical example where we use Salt to automate the setup of a multi-tier application stack that includes a web server and a database, handling the orchestration required to ensure they are correctly configured and dependent services are prioritized.

What is Orchestration in IaC?

Orchestration in IaC involves managing and automating complex workflows, where multiple steps or tasks need to be carried out in a specific order. Orchestration ensures that each component of an application stack, from databases to load balancers, is configured and deployed in the correct order with the necessary dependencies. Unlike basic configuration management, orchestration accounts for:

1. Dependency Management: Ensures that services are provisioned in the correct order. For example, a database must be ready before configuring the web server that relies on it.
2. State Management: Keeps track of the current state of each resource, allowing for state-based changes rather than re-provisioning everything.
3. Complex Workflows: Manages multi-step and conditional workflows, enabling processes like scaling, failover, and multi-region deployments.

Key Concepts in Advanced IaC

1. State Management: In IaC, managing state refers to keeping a record of infrastructure configurations at a given point in time. This allows for reliable updates and rollbacks and is critical for ensuring consistency in deployments. Salt uses "state files" to define desired configurations.
2. Handling Dependencies: Dependencies between services are defined to ensure that components dependent on each other are configured in the correct sequence. For example, ensuring that a database is operational before configuring an application server.
3. Complex Workflows: Advanced orchestration tools support conditional steps, loops, error handling, and retry mechanisms, which are essential for managing large, distributed systems.

SaltStack Overview

SaltStack (often referred to as Salt) is a powerful orchestration and configuration management tool that automates infrastructure at scale. Its key components include:

• States: Declarative descriptions of the desired configuration.
• Pillars: Data structures that store configuration data for targeted nodes.
• Grains: Metadata about the system (e.g., OS type, IP address) that Salt uses to dynamically target configurations.
• Runners: Execution modules that coordinate larger workflows, especially useful for complex orchestration tasks.

Salt offers flexible state management and orchestration capabilities, making it ideal for managing complex environments and dependencies between services. For larger environments, Puppet can complement Salt with strong configuration drift management and advanced reporting, though here, Salt will handle the orchestration.

Practical Example: Multi-Tier Application Setup with SaltStack

In this example, we’ll use SaltStack to automate the setup of a basic multi-tier application stack consisting of a web server and a database server. The orchestration will configure dependencies to ensure that the database is fully operational before the web server attempts to connect.

Prerequisites

1. SaltStack Installed: Install Salt on a master server, and ensure Salt minions (agents) are installed on each node.
2. Multi-Tier Setup: Provision two servers (or containers) for a web server and a database server.
3. Basic Network Configuration: Ensure that the web and database servers can communicate over the network.

Step 1: Define State Files

Create state files that describe the desired configuration for each component of our application stack:

1. Database State File: This file will install and configure the database.

# /srv/salt/db.sls
mysql-server:
  pkg.installed: []

mysql-service:
  service.running:
    - name: mysql
    - require:
      - pkg: mysql-server

# Ensure the database is created
myapp-db:
  mysql_database.present:
    - name: myapp
    - require:
      - service: mysql-service        

2. Web Server State File: This file will install and configure the web server.

# /srv/salt/web.sls
apache2:
  pkg.installed: []

apache-service:
  service.running:
    - name: apache2
    - require:
      - pkg: apache2

# Configure web app to connect to the database
web-app-config:
  file.managed:
    - name: /etc/webapp/config.yaml
    - source: salt://webapp/config.yaml
    - require:
      - service: apache-service        

Step 2: Orchestrate Dependencies Using Requisite System

To ensure that the web server setup depends on the database being operational, Salt's "requisite" system allows you to specify order dependencies:

# /srv/salt/orchestrate.sls
include:
  - db
  - web

web-service-start:
  cmd.run:
    - name: systemctl start apache2
    - require:
      - cmd: db-service-start        

Step 3: Running the Orchestration

Execute the orchestration on the Salt master to deploy the application stack across your servers:

salt-run state.orchestrate orchestrate        

This command will sequentially apply the states defined in the orchestrate.sls file, ensuring that the database is configured and running before the web server is started.

This command will sequentially apply the states defined in the orchestrate.sls file, ensuring that the database is configured and running before the web server is started.

Advanced Orchestration Use Cases

Here are additional scenarios where Salt's orchestration capabilities excel:

1. Blue-Green Deployments: Using Salt's orchestrate module, you can manage blue-green deployments, reducing downtime by directing traffic to a new environment after testing.
2. Zero-Downtime Upgrades: Salt can handle rolling updates, ensuring that only a subset of nodes are updated at a time, allowing services to continue operating during deployments.
3. Multi-Region Deployments: Salt orchestrates across multiple regions, ensuring consistent configuration across geographical zones, which is particularly useful for globally distributed applications.

Comparing Salt and Puppet for Orchestration

Both Salt and Puppet can manage configurations, but they offer different approaches:

• SaltStack: Known for its reactive, event-driven architecture, Salt can immediately respond to state changes, making it suitable for fast-paced environments that require real-time orchestration.
• Puppet: Better suited for environments needing a strong compliance framework. Puppet’s reporting and configuration drift capabilities make it ideal for tracking changes and maintaining compliance across large-scale infrastructures.

Advanced provisioning and orchestration with IaC tools like Salt provide infrastructure teams with robust solutions for managing complex, dynamic environments. Salt's event-driven architecture, state management, and flexibility make it an excellent choice for multi-tier application deployment, dependency management, and sophisticated orchestration workflows.