Fly.io runs containerised applications globally with a unique WireGuard-based private network. These exercises cover the Machines API, app configuration, persistent storage, and networking concepts essential for production deployments.
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1 / 5
At standup, a colleague asks what the Machines API is in Fly.io. What is the correct answer?
The Fly Machines API is a low-level REST API that lets you manage individual Fly Machines programmatically. You can create, start, stop, update, and destroy machines using HTTP requests — without the CLI or fly.toml. It is useful for dynamic workloads where you want to spin up short-lived VMs on demand, such as per-user compute, CI runners, or preview environments.
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During a PR review, a teammate asks what fly.toml configures. Which answer is most complete?
fly.toml is Fly.io's app configuration file. It declares the app name, primary region, HTTP services (internal port, concurrency limits, health checks), process groups, volume mounts, environment variables, and deploy strategies (rolling, canary, etc.). It is the primary way to configure how flyctl deploy builds and runs your app, though the Machines API can override or supplement it.
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In a design review, the team discusses persistent volumes on Fly.io. A junior engineer asks what happens to data on a volume if the machine is destroyed. What is correct?
Fly Volumes are persistent block storage that exist independently of the machines they are attached to. If you destroy a machine and create a new one in the same region, you can attach the existing volume and all data is intact. Volumes must be explicitly deleted to remove data — machine destruction alone does not delete them. This makes volumes safe for databases and stateful workloads on Fly.io.
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An incident report shows two machines in different regions cannot reach each other on internal ports. A senior engineer asks what private networking on Fly.io uses. What is correct?
Fly.io's private networking is built on WireGuard. Every machine in an organisation is assigned a private IPv6 address on the fdaa::/8 prefix. Machines resolve each other using .internal DNS names (e.g., my-app.internal) through Fly's internal DNS, and traffic travels over the encrypted WireGuard overlay — not the public internet. This works across regions automatically without any extra configuration.
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During a code review, a senior engineer asks what the concurrency settings in a Fly.io service configuration do. What is correct?
Fly.io service concurrency settings define two thresholds for load balancing. The soft_limit signals Fly's proxy to prefer routing new requests to less-loaded machines. The hard_limit is the maximum — once reached, the machine stops accepting new connections and Fly routes traffic elsewhere. Setting these correctly prevents any single machine from being overwhelmed and enables smooth horizontal scaling.
What does the "Fly.io Machines API Vocabulary" vocabulary exercise cover?
This exercise tests real IT vocabulary related to fly.io machines api vocabulary through 5 multiple-choice questions, each built from realistic workplace sentences rather than abstract definitions.
Is this vocabulary exercise free to use?
Yes. Every exercise on CoderSlingo, including this one, is completely free — no account, sign-up, or payment required.
How many questions does this exercise have?
This exercise has 5 questions. Each one shows a real-world sentence or scenario with multiple-choice options and an explanation once you answer.
What happens after I answer a question?
You'll see immediate feedback showing whether your answer was correct, along with a short explanation of why — then a button to move to the next question, and a full results screen at the end.
Can I retry the exercise if I get questions wrong?
Yes. Once you reach the results screen, click "Try again" to reset your answers and go through the exercise from the start as many times as you like.
Do I need to create an account to take this exercise?
No account is needed. Your answers are scored in your browser during the session — nothing is saved to a server, so you can jump straight in.
Is my progress saved if I leave the page?
No — progress within an exercise resets if you navigate away or reload. Each exercise is short enough to complete in a few minutes in one sitting.
Are these vocabulary exercises connected to other topics?
Yes — this module shares real-world context with 14 other vocabulary modules. See "Related vocabulary" below to keep building a connected skill set.
How is this different from reading a glossary or blog article?
Exercises like this one are active recall drills — you have to choose the correct term or phrasing yourself, which builds retention faster than passively reading a definition.
Where can I find more vocabulary exercises?
Browse the full Vocabulary exercises hub for hundreds of modules covering Agile, DevOps, security, databases, architecture, and more — organised by IT role and skill.