Quick Answer
The answer is to use the 'dnsConfig' property in the container group configuration. This is correct because Azure Container Instances manages the network stack at the container group level, meaning individual container-level DNS settings from a Dockerfile or environment variables are ignored; the dnsConfig property in your ARM template or deployment JSON allows you to specify an array of custom DNS server IPs and optional search domains that apply uniformly to all containers in the group. On the AZ-204 exam, this tests your understanding of how ACI abstracts networking—a common trap is assuming you can set DNS via environment variables or Dockerfile directives, which the platform overrides. Remember the memory tip: "Group DNS, not container DNS"—the configuration must be applied to the entire container group, not to individual instances.
This AZ-204 practice question tests your understanding of develop azure compute solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are running a containerized application on Azure Container Instances. The application requires a custom DNS server. How should you configure this?
Set the DNS server in the container's environment variables
Why wrong: Environment variables do not set DNS servers.
Use the 'dnsConfig' property in the container group configuration
dnsConfig sets custom DNS servers for the container group.
Set the restart policy to 'Always'
Why wrong: Restart policy does not affect DNS.
Configure the DNS server in the Dockerfile
Why wrong: Dockerfile does not configure runtime DNS for ACI.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use the 'dnsConfig' property in the container group configuration
Azure Container Instances (ACI) supports custom DNS server configuration at the container group level via the 'dnsConfig' property in the deployment JSON or ARM template. This property allows you to specify an array of DNS server IP addresses and optional search domains, which are applied to all containers within the group. Environment variables cannot override DNS resolution, and the Dockerfile's DNS settings are ignored by ACI because the container group's network stack is managed by the Azure platform.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Set the DNS server in the container's environment variables
Why it's wrong here
Environment variables do not set DNS servers.
Use the 'dnsConfig' property in the container group configuration
Why this is correct
dnsConfig sets custom DNS servers for the container group.
Related concept
Read the scenario before looking for a memorised answer.
Set the restart policy to 'Always'
Why it's wrong here
Restart policy does not affect DNS.
Configure the DNS server in the Dockerfile
Why it's wrong here
Dockerfile does not configure runtime DNS for ACI.
Common exam traps
The trap here is that candidates assume DNS configuration can be set via environment variables or the Dockerfile, similar to how they might configure it in a standalone Docker environment, but ACI requires explicit container group-level network settings that override any container-level DNS directives.
Detailed technical explanation
Under the hood, ACI uses a per-container-group virtual network interface with its own DNS resolver settings. The 'dnsConfig' property maps directly to the Linux 'resolv.conf' file inside the container, allowing you to specify up to 5 DNS servers. In a real-world scenario, if your containerized app needs to resolve internal corporate domain names (e.g., 'myapp.internal.company.com'), you must set the custom DNS server via 'dnsConfig' to ensure queries are forwarded to your private DNS resolver rather than the default Azure-provided DNS (168.63.129.16).
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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FAQ
Develop Azure compute solutions — This question tests Develop Azure compute solutions — Read the scenario before looking for a memorised answer..
The correct answer is: Use the 'dnsConfig' property in the container group configuration — Azure Container Instances (ACI) supports custom DNS server configuration at the container group level via the 'dnsConfig' property in the deployment JSON or ARM template. This property allows you to specify an array of DNS server IP addresses and optional search domains, which are applied to all containers within the group. Environment variables cannot override DNS resolution, and the Dockerfile's DNS settings are ignored by ACI because the container group's network stack is managed by the Azure platform.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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