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Ansible vs. Terraform Vs Pulumi: A Guide to IaC Tools

As the DevOps industry gains momentum, tools like Ansible and Terraform are following suit. As organizations are implementing and building processes with Infrastructure as Code (IaC), tools such as Ansible and Terraform are enabling companies to deploy code and infrastructure with complex requirements more easily. If you are looking to improve automation within your organization, Ansible and Terraform are powerful tools to integrate. However, which tool will serve you best?

Infrastructure as Code (IaC) is the process of managing and provisioning computer data centres through machine-readable files as opposed to physical hardware configuration. Shifting away from manual configuration, using IaC not only provides speed, but consistency, repeatability and scalability. Further IaC tools have added benefits in that they help reduce system inconsistencies, human error, loss of context and configuration drift. To make this shift, we have many tools at our disposal- Ansible and Terraform being a few powerful options. But what distinguishes these tools from one another, and is one IaC tool a better option than the next? As we navigate through these two tools, keep in mind that each tool was created with a specific purpose in mind which may ultimately sway your decision.


Ansible vs Terraform: Similarities

Before we delve into the key differences between the IaC tools Ansible and Terraform, we should note a few of their similarities. First to note is the idea of IaC tools having a master machine or being masterless. That is, whether a master server is run to store the state of the infrastructure, along with distributing updates. In this regard, both Ansible and Terraform are masterless by default. Ansible functions by directly connecting to each server over SSH, thus not requiring the running of any additional infrastructures. Terraform communicates with cloud providers using the cloud provider’s APIs, also not requiring any additional infrastructures.

Additionally, we have the idea of agent vs agentless. Some tools require you to install agent software on each server that you configure. The agent’s purpose is to install the latest configuration management updates. In this regard both Ansible and Terraform are agentless. Now that we’ve noted a few similarities between these two IaC tools, let’s dive into the differences that distinguish Ansible from Terraform.

Ansible vs Terraform: Key Differences

Orchestration vs Configuration Management (CM) Tools:

In choosing the right IaC tool and in identifying the key differences between Ansible and Terraform, the first distinguishing factor is whether they are orchestration or configuration management tools. Within DevOps, an orchestration tool ensures that an environment is within a specific desired state. Terraform falls into this category. Specifically, it stores the state of an environment, and if the system were to encounter a malfunction, Terraform automatically computes and restores the system after reloading. Thus it provides a good foundation for recovery should a malfunction occur. 

On the other hand, a configuration management tool was created with the purpose to install and manage software on existing server instances. A configuration management tool maintains all the components of an environment in working condition. Ansible is mainly a configuration management tool and ensures that each component in the environment functions properly and does not have any damage. One key distinguishing factor between Terraform and Ansible, is that as opposed to replacing an entire infrastructure, Ansible functions by simply repairing the issue at hand. One fact to note is that Ansible can also function as an orchestration tool, though in this respect Terraform may be a better option.

Declarative vs Procedural Language Style:

When performing their functions, we also want to know how these tools are able to execute them. This is where procedural vs declarative language styles come into play. With a declarative language, code is written out that specifies the desired end state, and the IaC tool then automatically determines the steps necessary to achieve that end state in the most efficient way possible. Terraform is one such IaC tool that uses a declarative language style. 

With a procedural language style, code is written out that outlines a specific set of steps that are required in order to reach the desired end state. In this case, Ansible can be considered a hybrid in this aspect as well. It performs procedural-style configuration; however, with the aid of modules, it can utilize the declarative-style as well. In comparing declarative and procedural language style, declarative tools may be more beneficial to those with a programming background, while procedural tools may be more beneficial to those with a scripting background.

Mutable Infrastructure vs Immutable Infrastructure:

Traditional server environments are typically mutable. A mutable infrastructure allows for updates and modifications to be made after deployment of software. In this case, Ansible defaults to a mutable infrastructure paradigm. However do note that over time, as we continue to add more and more updates, each server builds a unique history of changes. This may lead to the issue of configuration drift. Configuration drift refers to the idea that each server becomes slightly different from the other, which can lead to configuration bugs that may be difficult to diagnose. 

On the other hand, in utilizing a tool like Terraform, you are looking at an immutable infrastructure. Specifically, one wherein servers are never modified after they are deployed. Instead, whenever a change or update is required, new servers with the desired changes are built and deployed. That is, new servers replace existing ones. This approach comes with various benefits, including minimizing the risk of configuration drift bugs and knowing exactly what software is running on a server.


What is Pulumi?

Pulumi is an infrastructure as code tool used for creating, deploying, and managing infrastructure. In comparing Terraform and Pulumi, we see that they share key similarities. They can both be used to provision and manage infrastructure across various cloud providers. For instance, both tools support various cloud providers including AWS, Azure and Google Cloud. Pulumi can work with both traditional infrastructure as well as more modern architectures- whether it be virtual machines, containers, etc.

However, while Pulumi shares key similarities with Terraform, we can also see that it offers other features that distinguish the two tools. One key difference is the programming language being used. An IaC tool such as Terraform requires the use of its own custom declarative language called HashiCorp Configuration Language (HCL).

Meanwhile, a tool like Pulumi has the advantage in that it can support various familiar languages. With Pulumi, you can define infrastructure using already familiar languages such as Python, JavaScript, TypeScript, etc. Thus, you can keep using conditionals, loops, and functions which can make this tool appealing. Thus, rather than learning HCL, you can use leverage already familiar tools and fast-track your approach and maximize productivity.

Whether you want to use Pulumi straight away, or to test out the waters by slowly transitioning into this platform, Pulumi can be adapted by either method. With Pulumi, you have the added option of starting from Terraform and using it side by side as you transition towards Pulumi. That is, your existing resources that were provisioned using other tools can co-exist as you provision new infrastructure with Pulumi. So we can begin to see just the flexibility of incorporating an IaC tool like Pulumi truly can provide. While this article just begins to describe the capabilities of Pelumi, we can see that with similar features to Terraform along with its added flexibility to developers, it really is a true contender.




Overall, both Ansible and Terraform offer key benefits that allow organizations to become that more efficient and scalable as they grow. Ansible and Terraform, while offering a few similarities, also have key differences as each tool is made with a specific intent and purpose in mind. So, in the end as you sift through the differences in deciding on choosing either Ansible or Terraform, your system requirements and goals are what may ultimately help you choose the right Infrastructure as Code tool.

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