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In cloud deployments you typically choose between virtual machines (VMs) and containers. This article compares the two approaches and then explains Azure Container Instances (ACI): a fast, PaaS way to run containers in Azure without managing VMs. VMs are the traditional virtualization model. A hypervisor (Type 1 on hardware or Type 2 on a host OS) runs one or more VMs. Each VM contains the application, required binaries and libraries, and a full guest operating system. This provides strong isolation and security at the cost of higher resource usage and slower start times. Containers provide a lighter-weight model: they package your application and its runtime dependencies but share the host OS kernel. A container runtime isolates processes using OS-level primitives (namespaces, cgroups), so containers are smaller and start much faster — ideal for rapid scaling and microservices. A simple analogy: a VM is like a house with dedicated utilities; containers are like apartments in a building that share infrastructure but remain isolated.
A diagram comparing virtual machines and containers. It shows VMs include a guest OS plus libs/binaries and apps running on a hypervisor, while containers share the host OS via a container runtime and contain only apps and libs.
Detailed comparison What is Azure Container Instances (ACI) ACI abstracts the underlying infrastructure so you can run containers without managing VM hosts. It integrates with Azure networking and storage and is offered as a Platform-as-a-Service (PaaS).
ACI is a PaaS offering: you don’t manage the VM OS. Under the hood Azure manages container hosts, runtimes, and virtual networking so you can focus on running containers.
Key features and benefits
  • Fast startup: instances typically start in seconds, suitable for short-lived tasks and bursty workloads.
  • Public endpoints: ACI can assign a public IP and DNS label so containers are accessible from the internet (good for simple web apps or APIs).
  • Isolation: each container group runs isolated from other tenants and container groups.
  • Scalability: scale by creating additional container instances; for advanced scheduling and stateful orchestration, integrate with orchestration solutions.
  • Persistent storage: mount Azure storage such as Azure Files for persistent data. (Azure Disk support is limited to specific scenarios/regions.)
  • Virtual Network (VNet) integration: deploy containers into a VNet to communicate securely with other Azure resources.
  • Registry support: pull images from Quickstart images, Azure Container Registry, Docker Hub, or other registries.
Deploying a container instance from the Azure Portal
  1. In the Azure Portal, search for “Container Instances” and click Create.
  2. Configure basic settings: resource group, container instance name (for example aci-web-01), region, SKU/availability options, and the container image source. You can choose Quickstart images (for example nginx), your Azure Container Registry, Docker Hub, or third-party registries.
  3. Networking tab: choose Public, Private (VNet), or None. Provide a DNS name label and select ports to expose.
  4. Advanced tab: set the restart policy (Always, OnFailure, Never) and provide a command override for custom startup commands.
  5. Validate and click Create. Deployments often complete in seconds to a minute depending on the image and configuration.
Portal screenshot — Networking tab
A screenshot of the Microsoft Azure "Create container instance" wizard open to the Networking tab, showing options for Public/Private/None networking, a DNS name label field, and port configuration (port 80/TCP). The bottom has navigation buttons like "Review + create", "Previous", and "Next: Advanced."
After deployment When deployment finishes, open the container instance resource. The Overview shows essentials such as resource group, status, public IP (if assigned), SKU, and OS type. Monitoring charts display CPU and memory usage. You can view logs, inspect running containers, and — where supported — open an interactive terminal for debugging.
A Microsoft Azure portal screenshot showing the Overview page for a container instance named "aci-web-01," with essentials like resource group, status (Running), public IP, SKU and OS type. Below are CPU and Memory usage charts and a left-hand navigation menu for settings and monitoring.
Interactive connect and debugging ACI supports viewing logs and connecting to a shell (when the image supports it). The portal shows a Connect/Console tab where you can run commands inside the running container for troubleshooting or demonstration purposes.
A screenshot of the Microsoft Azure portal showing a container instance named "aci-web-01" running an nginx image, with the "Connect" tab open and a "Choose Start Up Command" dialog visible.
Example: editing the default nginx index page inside a running container (demo only)
Editing files inside a running container is useful for quick debugging or demos, but it’s not recommended for production. For production changes, bake modifications into your container image and use persistent volumes for application data.
Summary Azure Container Instances provides a simple, fast PaaS option for running containerized workloads in Azure without managing VM infrastructure. Use ACI for short-lived, bursty, or internet-facing workloads that need rapid startup and straightforward deployment. For more advanced orchestration, stateful workloads, or complex scheduling, integrate ACI with orchestration platforms or consider Azure Kubernetes Service (AKS).

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