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Networking — IP plan & private DNS

The address space matches the Infrastructure Architecture document (192.168.0.0/16, agent subnet 192.168.0.0/24, private-endpoint subnet 192.168.1.0/24). Everything else fits around those two fixed values.

Subnet plan

Subnet CIDR Delegation / purpose
snet-agent 192.168.0.0/24 Delegated to Microsoft.App/environments. Foundry hosted-agent network injection. Dedicated to this Foundry resource — cannot be shared.
snet-pe 192.168.1.0/24 Private endpoints for Foundry, Cosmos, AI Search, Storage, Key Vault, ACR. PE network policies disabled.
snet-aca 192.168.2.0/24 Delegated to Microsoft.App/environments. Internal ACA environment (UI, stubs, Toolbox, jobs).
AzureBastionSubnet 192.168.3.0/26 Azure Bastion (fixed name, /26 minimum).
snet-appsvc 192.168.4.0/24 Delegated to Microsoft.Web/serverFarms. Only used if the optional Web App is enabled.
snet-mgmt 192.168.5.0/24 Undelegated. Hosts the optional Windows jumpbox VM (Bastion target). Created always; VM only when deployJumpbox = true.

Jumpbox access path: external user → Azure Portal (Entra sign-in) → Bastion → jumpbox VM in snet-mgmt (RDP over TLS 443). The VM has no public IP; a NIC-level NSG allows RDP (3389) only from the Bastion subnet. A VM can't live in the delegated subnets (snet-agent, snet-aca, snet-appsvc) or in AzureBastionSubnet, which is why snet-mgmt exists.

Adjust any prefix via parameters/variables. Keep snet-agent and snet-pe on the two document-specified values unless you have a reason to move them.

Ingress / egress posture

  • No public ingress. The ACA environment is internal: true; every app uses internal-only ingress. Reach the UI and tools through Azure Bastion (VPN or ExpressRoute are drop-in alternatives).
  • Optional public edge for the UI (Front Door + WAF). When deployFrontDoor = true, Azure Front Door (Premium) fronts only the ui app over Private Link to the ACA environment (groupId: managedEnvironments) — the container app still has no public IP. The path is Internet → Front Door → WAF → Private Link → internal ILB → ui. This is additive: the internal Bastion/ILB path is unchanged, and the WAF (DRS 2.1 + Bot Manager
    • per-IP rate limit) plus optional EasyAuth Entra sign-in gate the public surface. Setup, the required Private Link approval, and back-out are in FRONTDOOR-EASYAUTH.md.
  • Private data plane. Storage, Cosmos, AI Search, Foundry, Key Vault, and ACR all have public network access disabled and are reached over private endpoints.
  • Egress (NAT gateway, optional). Because Azure retired default outbound access (Sept 30, 2025), a private subnet has no internet egress unless you provide one. The optional deployNatGateway flag (deploy_nat_gateway in Terraform) adds a NAT gateway + Standard public IP and associates it with snet-mgmt (jumpbox) and snet-aca (container apps). This is outbound-only SNAT — no inbound exposure, so the "no public ingress" posture is preserved. It's a deliberate deviation from strict no public egress; leave the flag off to keep zero outbound. The data tier never needs it (private endpoints), and ACA image pulls use the platform path regardless — so the flag only matters for the jumpbox's own browsing and the app's outbound API calls (e.g. the external news/rate feed).
  • For a fully controlled egress (allow-list specific FQDNs), replace the NAT gateway with an Azure Firewall + a route table (UDR) — heavier, left out to keep the POC simple.

Private DNS zones (linked to the VNet)

Zone Serves
privatelink.blob.core.windows.net Storage (blob)
privatelink.documents.azure.com Cosmos DB (Sql)
privatelink.search.windows.net AI Search
privatelink.vaultcore.azure.net Key Vault
privatelink.azurecr.io Container Registry
privatelink.openai.azure.com Foundry / AIServices
privatelink.cognitiveservices.azure.com Foundry / AIServices
privatelink.services.ai.azure.com Foundry / AIServices

The Foundry account private endpoint registers across all three AI zones — all three are required for full resolution. Validate DNS resolution from inside the VNet after deploy; an approved private endpoint with an unlinked zone resolves to a public IP and the call is rejected (a classic private-Foundry failure — see OPERATIONS.md).

Container Apps: internal env, ingress, and DNS

  • The ACA environment is internal (internal_load_balancer_enabled = true) with a private static IP — no public ingress.
  • Each app uses external: true ingress. On an internal environment this means "reachable from the VNet via the internal load balancer" — still private, not internet-facing. (external: false would make an app reachable only by other apps inside the environment, which is why VNet clients like the jumpbox get a 404.) With external: true the app FQDN is <app>.<envDefaultDomain> (no .internal.).
  • The template auto-creates a Private DNS Zone named the environment's defaultDomain (e.g. greenbay-xxxx.<region>.azurecontainerapps.io), a * A record → the env's static IP, and a VNet link (modules/aca-private-dns.bicep / the aca_* resources in compute.tf). Without it, app FQDNs don't resolve from inside the VNet.
  • Test from an in-VNet host (jumpbox) using the exact FQDN from az containerapp show … --query properties.configuration.ingress.fqdn — don't hand-type it.

Region

VNet and Foundry must be in the same region, and that region must support Foundry hosted agents. Default swedencentral. The 192.168.x space is a private (RFC 1918) range; confirm it doesn't overlap any peered network or reserved range before you deploy.