Hire the Top 3% of Freelance Docker Developers

Demand for Docker Developers Has Never Been Higher

According to the Stack Overflow 2023 Developer Survey, 57% of professional developers use Docker, and most respondents want to use Docker next year compared to all “other tool” options. Docker’s rising popularity is likely a result of its versatility; it allows engineers to package complex applications and their dependencies into a minimally sized, cross-platform format. This packaging improves reliability, performance, and accelerates time to market by providing a consistent environment for testing, deploying, and distributing software.

When used correctly, Docker can accelerate the time to production of a software product and boost team productivity. However, when used incorrectly, it can, at best, have no impact, and, at worst, cause crashes in your production environment. This hiring guide explains how a skilled Docker developer can be a valuable asset on development teams and outlines the specific attributes that separate expert developers from average ones.

The guide walks you through how to write job posts that will attract qualified candidates, craft relevant interview questions, and assess an applicant’s expertise, so you can hire a Docker developer who can help boost your business’s productivity by simplifying the development, deployment, and distribution of your products.

What attributes distinguish quality Docker Developers from others?

The use of Docker is nearly ubiquitous, so most developers will have interacted with or created Dockerfiles. However, a standout Docker developer needs to have a deeper understanding of Docker and its multitude of components.

The complexity of modern software development necessitates that, in addition to expertise in Docker and its components, developers need to understand complementary technologies and software development principles at large. Their role goes beyond simply writing Dockerfiles or running containers—an expert Docker developer is crucial for building efficient, scalable, secure, and robust software solutions.

In addition, Docker developers need to be well-rounded professionals who operate effectively in a DevOps environment, where working with other teams is essential.

Complementary technology skills Docker developers should have

All Docker developers will have experience with command line interfaces (CLIs) because Docker operates primarily via the command line, but working with Docker involves more than just mastering the CLI. A skilled developer will have broader experience with multiple architectures and programming languages.

Here are complementary skills a Docker developer should be proficient in:

• Scripting – Docker tasks can often be automated using scripts, so a good grasp of scripting languages like Bash, Python, and Ruby is very helpful. Furthermore, Docker works with a single entry point, so it’s a common practice to make this entry point a script, which makes the startup process more flexible.
• Application development – Since Docker is used to containerize applications, developers should have a good understanding of application development in your app’s main language (e.g., Java, Python, Ruby, or C#). That way, despite a lack of lower-level programming experience, they can quickly debug configuration issues, including those related to bootstrapping and dependency management.
• Infrastructure as Code (IaC) – Tools like Terraform and AWS CloudFormation can be used in conjunction with Docker to automate testing, infrastructure creation, and management, and they are extremely useful for version control and rollbacks.
• Continuous Integration/Continuous Deployment (CI/CD) – Docker plays a crucial role in CI/CD pipelines, so familiarity with tools like GitHub Actions, Circle CI, Jenkins, and GitLab CI is a big plus.
• Networking – Networking can play a crucial role in several infrastructures to make intercontainer communication possible and restrict it for security purposes.
• Orchestration – Although Docker containers can be deployed as singular entities, it’s more common to deploy a cluster of them. Knowledge of orchestration tools such as Kubernetes, Docker Compose, Rancher, and Docker Swarm can be extremely useful for smooth deployment and maintenance.

A highly skilled Docker developer doesn’t merely manage containers. They apply a set of strategies and practices that streamline development, deployment, and distribution, thereby increasing productivity, reducing costs, and ensuring a smoother, more reliable software delivery pipeline.

How can you identify the ideal Docker Developer for you?

Essential to any Docker developer’s skillset is proper management of Docker images—the lightweight, stand-alone, executable packages central to Docker usage. Expert Docker developers understand the best practices needed for managing images effectively, from using multistage builds to reduce image size and build time to properly tagging and versioning images for easier version control. While experts excel in building great Docker infrastructure, less experienced developers may unwittingly create slow builds and bad caching.

Another key attribute of a skilled Docker developer is experience in orchestrating Docker services with tools like Docker Compose, Docker Swarm, or Kubernetes. Docker Compose is the simplest, and it’s useful to run basic containers and network infrastructures. Kubernetes and Docker Swarm (which is simpler than Kubernetes) are called orchestration tools because they allow advanced customization and features such as load balancing and autoscaling.

Although the top cloud providers (AWS, Google Cloud Platform, and Microsoft Azure) normally have multiple managed services to run container workloads, skills in orchestration tools are strongly recommended, especially if you don’t already have an infrastructure in place.

Docker’s networking management is another aspect to consider. Whereas a novice Docker developer will know only the basics of networking for local development, a senior-level developer will grasp the nuances and know when to use various networking modes, such as bridge, host, none, and overlay. Understanding these modes and applying the right one for the task at hand is crucial for the network performance of the containers and for security when containers require restricted access.

There are also platform-specific services, like AWS Fargate and Google Kubernetes Engine, which are inspired by Kubernetes but require their own sets of skills. If your project will need to use one of these services, include it in the project description and prioritize candidates who have that experience.

Equally important is managing data persistence within Docker. Containers are ephemeral by nature, meaning all changes made within a container are lost once it stops being used. However, many applications require some form of data persistence. Docker offers solutions for this through the use of volumes, bind mounts, and temporary file system volumes. Each method has its own advantages and use cases, so it’s important to keep these issues in mind when choosing among Docker Cloud hosting services, as they may have limitations.

Ultimately, the best Docker developer for your project would have extensive Docker experience and specialized knowledge of your industry and tech stack. And where gaps exist in your infrastructure, you’ll want someone who has done the initial setup of the specific pieces needed to fill them—not someone who has merely maintained the results of someone else’s work. You should also look for candidates who have collaborated well with other teams in a DevOps role. Someone with these attributes will be able to quickly improve the structure of your project and its deployment, lower your infrastructure costs, and provide business-specific advice.

How to Write a Docker Job Description for Your Project

When writing a Docker job description, it’s essential to specify the exact responsibilities and requirements for your project. First of all, you are probably looking for a DevOps engineer specializing in Docker, so make sure to include those keywords, as suggested in our Docker developer job description template, as potential candidates will be looking for them. You should also include responsibilities like maintaining Docker images, optimizing Dockerfiles, and setting up CI/CD pipelines.

In describing the job requirements, in addition to a strong understanding of Docker, you can list complementary skills based on your project’s needs. A description of the project, the stack being used, and how it’s deployed (or will be deployed) are all important pieces of information to include to attract and filter the best candidates.

What are the most important Docker interview questions?

A Docker expert should be able to articulate the benefits of Docker, but Docker interview questions should go beyond the fundamentals to assess the candidate’s understanding of complementary technologies and problem-solving skills. To help you evaluate candidates from a technical perspective and more broadly, here are examples of specific questions to consider asking, as well as the kind of information qualified candidates should provide in their answers:

What are the advantages of using Docker in a development environment?

Let’s start by answering this question: “What does Docker do?” Docker simplifies and connects the entire software development lifecycle by encapsulating the application and its dependencies. This naturally results in a clean, well-structured project environment right from its inception, which eliminates the “works on my machine” problem—a time-consuming issue that can recur often. Therefore, Docker’s containerization drastically reduces the time spent on setting up application environments and enables faster, more reliable development and simpler deployment.

What are the key differences between Docker and Kubernetes?

Docker is a software suite used to create lightweight, standalone, and executable packaged container images.

Kubernetes is a cloud-native orchestration system that can provide extra features like monitoring, security, high availability, and resource management. It’s flexible enough to run the simplest or most complex workloads on cloud or on-premise environments.

Can you explain the differences between Docker images and Docker containers?

Docker images are read-only templates that contain a snapshot of an application and its dependencies along with everything a company needs to run a piece of software—including application code, runtimes, system tools, system libraries, and settings. In contrast, Docker containers are runtime instances of Docker images. When you run an image, it becomes a container.

When have you used Docker in a production environment? Where and how was it deployed? Can you describe the challenges you faced and how you addressed them?

This is a useful question to get a sense of the candidate’s capabilities and understand their deployment experience. Docker can be hosted in several ways through specialized services or directly on instances, and each will bring different advantages and challenges. An experienced candidate should be able to describe this process clearly and in great detail.

Have you worked on a similar project that used Docker? What were the specific challenges? What did you learn from it?

Each tech stack has its own unique requirements and challenges. A developer with previous experience should be able to accurately describe some issues they encountered or some specifics that made it different from other stacks.

Can you explain what multistage builds are useful for?

Multistage builds enable the creation of light and efficient production images by using separate stages for building and running an application within a single Dockerfile. They allow developers to use one stage for compiling or building an application with all necessary dependencies and tools, and another stage to bundle only the built artifacts and necessary runtime into a final image, thus reducing the image size and enhancing security.

Can you explain the advantages of using parent images?

Similar to multistage builds, if there are libraries or code common to multiple images, you can create parent images that are inherited by all their child images. This way, the core requirements don’t need to be rebuilt and cached in multiple images. This is a core aspect of Docker images because most images don’t start empty—they inherit prebuilt images such as Node.js-, Python-, or Rust-ready environments.

What’s the difference between horizontal and vertical scaling, and when do you use one or the other?

Horizontal scaling is easier, but it works only when the container can be duplicated without any issues. For example, it’s common for computationally heavy loads, where each container is independent. On the other hand, vertical scaling is used when the container cannot be duplicated easily, usually due to a resource bottleneck. A typical example would be databases, where you can’t simply duplicate the database. Instead, a developer would need to scale the container itself; for example, by granting more resources.

Why do companies hire Docker Developers?

Docker is a must-have for any modern stack because it’s the glue that simplifies and connects the entire software development lifecycle, making the whole process more efficient and less error-prone. It offers a robust platform for application isolation, packaging, and deployment, making it a critical tool for businesses striving for efficient and scalable software delivery. Companies hire Docker developers to realize these substantial benefits.

Docker has emerged as an industry standard, accepted readily across most cloud platforms. This eliminates the need for extra packaging and resolves issues caused by differences between software environments, simplifying the path from development to deployment. By encapsulating the application and its dependencies into a single unit, Docker ensures that the application behaves the same way during production as it did during development, thus minimizing deployment surprises and debugging time.

Additionally, due to their independent structure, Docker-based solutions tend to be inherently scalable. Most applications have peak and low periods of use, and Docker frameworks, such as Kubernetes, can monitor the load and manage it by adding and removing containers as needed. This lowers the probability of crashes and makes deployment cost-efficient.

From a distribution perspective, Docker’s widespread adoption makes it a straightforward choice, as it’s simple to install the application on client machines regardless of their underlying operating systems. The simplicity and reliability of distribution means your application can reach end users more efficiently.

What are the benefits of hiring a Docker Developer?

Having a Docker expert on board can bring substantial business benefits by not only simplifying development but also boosting productivity. Using Docker properly can also contribute to more efficient resource management, lower infrastructure costs, and better collaboration among developers, QA, and operations teams—ultimately leading to a DevOps culture.

The technical content presented in this article was reviewed by Felipe Rodrigues Maia.