169 lines
7.1 KiB
Markdown
169 lines
7.1 KiB
Markdown
# On-prem DNS and Google Private Access
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This example leverages the [on prem in a box](../../modules/on-prem-in-a-box) module to bootstrap an emulated on-premises environment on GCP, then connects it via VPN and sets up BGP and DNS so that several specific features can be tested:
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- [Cloud DNS forwarding zone](https://cloud.google.com/dns/docs/overview#fz-targets) to on-prem
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- DNS forwarding from on-prem via a [Cloud DNS inbound policy](https://cloud.google.com/dns/docs/policies#create-in)
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- [Private Access for on-premises hosts](https://cloud.google.com/vpc/docs/configure-private-google-access-hybrid)
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The example has been purposefully kept simple to show how to use and wire the on-prem module, but it lends itself well to experimenting and can be combined with the other [infrastructure examples](../) in this repository to test different GCP networking patterns in connection to on-prem. This is the high level diagram:
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## Managed resources and services
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This sample creates several distinct groups of resources:
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- one VPC
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- one set of firewall rules
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- one Cloud NAT configuration
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- one test instance
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- one service account for the test instance
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- one service account for the onprem instance
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- one dynamic VPN gateway with a single tunnel
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- two DNS zones (private and forwarding) and a DNS inbound policy
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- one emulated on-premises environment in a single GCP instance
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## Cloud DNS inbound forwarder entry point
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The Cloud DNS inbound policy reserves an IP address in the VPC, which is used by the on-prem DNS server to forward queries to Cloud DNS. This address needs of course to be explicitly set in the on-prem DNS configuration (see below for details), but since there's currently no way for Terraform to find the exact address (cf [Google provider issue](https://github.com/terraform-providers/terraform-provider-google/issues/3753)), the following manual workaround needs to be applied.
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### Find out the forwarder entry point address
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Run this gcloud command to (find out the address assigned to the inbound forwarder)[https://cloud.google.com/dns/docs/policies#list-in-entrypoints]:
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```bash
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gcloud compute addresses list -project [your project id]
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```
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In the list of addresses, look for the address with purpose `DNS_RESOLVER` in the subnet `to-onprem-default`. If its IP address is `10.0.0.2` it matches the default value in the Terraform `forwarder_address` variable, which means you're all set. If it's different, proceed to the next step.
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### Update the forwarder address variable and recreate on-prem
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If the forwader address does not match the Terraform variable, add the correct value in your `terraform.tfvars` (or change the default value in `variables.tf`), then taint the onprem instance and apply to recreate it with the correct value in the DNS configuration:
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```bash
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tf apply
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tf taint 'module.vm-onprem.google_compute_instance.default["onprem-1"]'
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tf apply
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```
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## CoreDNS configuration for on-premises
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The on-prem module uses a CoreDNS container to expose its DNS service, configured with foru distinct blocks:
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- the onprem block serving static records for the `onprem.example.com` zone that map to each of the on-prem containers
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- the forwarding block for the `gcp.example.com` zone and for Google Private Access, that map to the IP address of the Cloud DNS inbound policy
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- the `google.internal` block that exposes to containers a name for the instance metadata address
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- the default block that forwards to Google public DNS resolvers
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This is the CoreDNS configuration:
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```coredns
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onprem.example.com {
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root /etc/coredns
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hosts onprem.hosts
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log
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errors
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}
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gcp.example.com googleapis.com {
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forward . ${resolver_address}
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log
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errors
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}
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google.internal {
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hosts {
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169.254.169.254 metadata.google.internal
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}
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}
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. {
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forward . 8.8.8.8
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log
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errors
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}
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```
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## Testing
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### Onprem to cloud
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```bash
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# connect to the onprem instance
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gcloud compute ssh onprem-1
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# check that the BGP session works and the advertised routes are set
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sudo docker exec -it onprem_bird_1 ip route |grep bird
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10.0.0.0/24 via 169.254.1.1 dev vti0 proto bird src 10.0.16.2
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35.199.192.0/19 via 169.254.1.1 dev vti0 proto bird src 10.0.16.2
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199.36.153.4/30 via 169.254.1.1 dev vti0 proto bird src 10.0.16.2
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199.36.153.8/30 via 169.254.1.1 dev vti0 proto bird src 10.0.16.2
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# get a shell on the toolbox container
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sudo docker exec -it onprem_toolbox_1 sh
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# test pinging the IP address of the test instance (check outputs for it)
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ping 10.0.0.3
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# note: if you are able to ping the IP but the DNS tests below do not work,
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# refer to the sections above on configuring the DNS inbound fwd IP
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# test forwarding from CoreDNS via the Cloud DNS inbound policy
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dig test-1.gcp.example.org +short
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10.0.0.3
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# test that Private Access is configured correctly
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dig compute.googleapis.com +short
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private.googleapis.com.
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199.36.153.8
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199.36.153.9
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199.36.153.10
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199.36.153.11
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# issue an API call via Private Access
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gcloud config set project [your project id]
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gcloud compute instances list
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```
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### Cloud to onprem
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```bash
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# connect to the test instance
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gcloud compute ssh test-1
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# test forwarding from Cloud DNS to onprem CoreDNS (address may differ)
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dig gw.onprem.example.org +short
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10.0.16.1
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# test a request to the onprem web server
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curl www.onprem.example.com -s |grep h1
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<h1>On Prem in a Box</h1>
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```
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## Operational considerations
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A single pre-existing project is used in this example to keep variables and complexity to a minimum, in a real world scenarios each spoke would probably use a separate project.
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The VPN used to connect to the on-premises environment does not account for HA, upgrading to use HA VPN is reasonably simple by using the relevant [module](../../modules/net-vpn-ha).
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<!-- BEGIN TFDOC -->
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## Variables
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| name | description | type | required | default |
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|---|---|:---: |:---:|:---:|
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| project_id | Project id for all resources. | <code title="">string</code> | ✓ | |
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| *bgp_asn* | BGP ASNs. | <code title="map(number)">map(number)</code> | | <code title="{ gcp = 64513 onprem = 64514 }">...</code> |
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| *bgp_interface_ranges* | BGP interface IP CIDR ranges. | <code title="map(string)">map(string)</code> | | <code title="{ gcp = "169.254.1.0/30" }">...</code> |
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| *ip_ranges* | IP CIDR ranges. | <code title="map(string)">map(string)</code> | | <code title="{ gcp = "10.0.0.0/24" onprem = "10.0.16.0/24" }">...</code> |
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| *region* | VPC region. | <code title="">string</code> | | <code title="">europe-west1</code> |
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| *resolver_address* | GCP DNS resolver address for the inbound policy. | <code title="">string</code> | | <code title="">10.0.0.2</code> |
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| *ssh_source_ranges* | IP CIDR ranges that will be allowed to connect via SSH to the onprem instance. | <code title="list(string)">list(string)</code> | | <code title="">["0.0.0.0/0"]</code> |
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## Outputs
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| name | description | sensitive |
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|---|---|:---:|
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| foo | None | |
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| onprem-instance | Onprem instance details. | |
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| test-instance | Test instance details. | |
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<!-- END TFDOC -->
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