ACI DNS Health Check

CloudBlue Connect EaaS extension that continuously monitors DNS resolution and TCP connectivity in Azure Container Instances (ACI).

Built to detect intermittent DNS failures like:

socket.gaierror: [Errno -3] Temporary failure in name resolution

How it works

A single schedulable (DNS Health Check) runs at a configurable interval and for each host:

1. Logs the container's /etc/resolv.conf (DNS server configuration)
2. Resolves the hostname via socket.getaddrinfo (same code path as urllib3/requests)
3. Attempts a TCP connect to port 443 to verify reachability beyond DNS
4. Logs timing and results with clear OK / WARN / FAIL prefixes
5. Returns success if all pass, fail with details if any host fails

Default hosts checked

Host	Why
api.partnercenter.microsoft.com	Microsoft Partner Center API
login.microsoftonline.com	Azure AD / Entra ID
graph.microsoft.com	Microsoft Graph API
management.azure.com	Azure Resource Manager
portal.azure.com	Azure Portal
google.com	Non-Microsoft DNS sanity check
cloudflare.com	Non-Microsoft DNS sanity check
dns.google	Non-Microsoft DNS sanity check

If the non-Microsoft hosts also fail, the problem is not Azure-specific.

Configuration

Extra hosts

Set the DNS_CHECK_EXTRA_HOSTS variable (comma-separated) via the Connect portal or as an OS environment variable:

srvc-7374-6941.ext.cloudblue.io,apix.ingrammicro.com

Schedule interval

Configure in the Connect portal under the extension's schedulable settings. Recommended: every 1 minute for catching intermittent failures.

Local development

1. Copy and fill in the env file:

   cp .dns_check_dev.env.example .dns_check_dev.env
   # Edit with your API_KEY, ENVIRONMENT_ID, SERVER_ADDRESS

2. Run:

   docker-compose up dns_check_dev

Example log output

INFO  ============================================================
INFO  DNS Health Check | 2026-03-25 18:35:04 UTC | 8 hosts
INFO  ============================================================
INFO  --- /etc/resolv.conf ---
INFO    nameserver 127.0.0.11
INFO  --- end resolv.conf ---
INFO    OK   | api.partnercenter.microsoft.com | DNS 88ms -> ['51.103.5.205'] | TCP 41ms
INFO    OK   | login.microsoftonline.com | DNS 17ms -> ['20.190.147.0', ...] | TCP 42ms
INFO    OK   | graph.microsoft.com | DNS 18ms -> ['20.190.177.152', ...] | TCP 45ms
INFO    OK   | management.azure.com | DNS 44ms -> ['4.150.240.10'] | TCP 48ms
INFO    OK   | portal.azure.com | DNS 49ms -> ['150.171.84.24'] | TCP 45ms
INFO    OK   | google.com | DNS 14ms -> ['192.178.218.100', ...] | TCP 111ms
INFO    OK   | cloudflare.com | DNS 16ms -> ['104.16.132.229', ...] | TCP 23ms
INFO    OK   | dns.google | DNS 18ms -> ['8.8.4.4', '8.8.8.8'] | TCP 30ms
INFO  ============================================================
INFO  Result: 8/8 passed
INFO  ============================================================

When a failure occurs:

ERROR   FAIL | api.partnercenter.microsoft.com | DNS 5002ms -> [Errno -3] Temporary failure in name resolution