# On-prem DNS and Google Private Access This example leverages the [on prem in a box](../../../modules/cloud-config-container/onprem) 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: - [Cloud DNS forwarding zone](https://cloud.google.com/dns/docs/overview#fz-targets) to on-prem - DNS forwarding from on-prem via a [Cloud DNS inbound policy](https://cloud.google.com/dns/docs/policies#create-in) - [Private Access for on-premises hosts](https://cloud.google.com/vpc/docs/configure-private-google-access-hybrid) 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: ![High-level diagram](diagram.png "High-level diagram") ## Managed resources and services This sample creates several distinct groups of resources: - one VPC with two regions - one set of firewall rules - one Cloud NAT configuration per region - one test instance on each region - one service account for the test instances - one service account for the onprem instance - two dynamic VPN gateways in each of the regions with a single tunnel - two DNS zones (private and forwarding) and a DNS inbound policy - one emulated on-premises environment in a single GCP instance ## Cloud DNS inbound forwarder entry point 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. ### Find out the forwarder entry point address Run this gcloud command to (find out the address assigned to the inbound forwarder)[https://cloud.google.com/dns/docs/policies#list-in-entrypoints]: ```bash gcloud compute addresses list --project [your project id] ``` 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. ### Update the forwarder address variable and recreate on-prem 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: ```bash tf apply tf taint 'module.vm-onprem.google_compute_instance.default["onprem-1"]' tf apply ``` ## CoreDNS configuration for on-premises The on-prem module uses a CoreDNS container to expose its DNS service, configured with foru distinct blocks: - the onprem block serving static records for the `onprem.example.com` zone that map to each of the on-prem containers - 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 - the `google.internal` block that exposes to containers a name for the instance metadata address - the default block that forwards to Google public DNS resolvers This is the CoreDNS configuration: ```coredns onprem.example.com { root /etc/coredns hosts onprem.hosts log errors } gcp.example.com googleapis.com { forward . ${resolver_address} log errors } google.internal { hosts { 169.254.169.254 metadata.google.internal } } . { forward . 8.8.8.8 log errors } ``` ## Testing ### Onprem to cloud ```bash # check containers are running sudo docker ps # connect to the onprem instance gcloud compute ssh onprem-1 # check that the VPN tunnels are up sudo docker exec -it onprem_vpn_1 ipsec statusall Status of IKE charon daemon (strongSwan 5.8.1, Linux 5.4.0-1029-gcp, x86_64): uptime: 6 minutes, since Nov 30 08:42:08 2020 worker threads: 11 of 16 idle, 5/0/0/0 working, job queue: 0/0/0/0, scheduled: 8 loaded plugins: charon aesni mgf1 random nonce x509 revocation constraints pubkey pkcs1 pkcs7 pkcs8 pkcs12 pgp dnskey sshkey pem openssl fips-prf gmp curve25519 xcbc cmac curl sqlite attr kernel-netlink resolve socket-default farp stroke vici updown eap-identity eap-sim eap-aka eap-aka-3gpp2 eap-simaka-pseudonym eap-simaka-reauth eap-md5 eap-mschapv2 eap-radius eap-tls xauth-generic xauth-eap dhcp unity counters Listening IP addresses: 10.0.16.2 169.254.1.2 169.254.2.2 Connections: gcp: %any...35.233.104.67,0.0.0.0/0,::/0 IKEv2, dpddelay=30s gcp: local: uses pre-shared key authentication gcp: remote: [35.233.104.67] uses pre-shared key authentication gcp: child: 0.0.0.0/0 === 0.0.0.0/0 TUNNEL, dpdaction=restart gcp2: %any...35.246.101.51,0.0.0.0/0,::/0 IKEv2, dpddelay=30s gcp2: local: uses pre-shared key authentication gcp2: remote: [35.246.101.51] uses pre-shared key authentication gcp2: child: 0.0.0.0/0 === 0.0.0.0/0 TUNNEL, dpdaction=restart Security Associations (2 up, 0 connecting): gcp2[4]: ESTABLISHED 6 minutes ago, 10.0.16.2[34.76.57.103]...35.246.101.51[35.246.101.51] gcp2[4]: IKEv2 SPIs: 227cb2c52085a743_i 13b18b0ad5d4de2b_r*, pre-shared key reauthentication in 9 hours gcp2[4]: IKE proposal: AES_GCM_16_256/PRF_HMAC_SHA2_512/MODP_2048 gcp2{4}: INSTALLED, TUNNEL, reqid 2, ESP in UDP SPIs: cb6fdb84_i eea28dee_o gcp2{4}: AES_GCM_16_256, 3298 bytes_i, 3051 bytes_o (48 pkts, 3s ago), rekeying in 2 hours gcp2{4}: 0.0.0.0/0 === 0.0.0.0/0 gcp[3]: ESTABLISHED 6 minutes ago, 10.0.16.2[34.76.57.103]...35.233.104.67[35.233.104.67] gcp[3]: IKEv2 SPIs: e2cffed5395b63dd_i 99f343468625507c_r*, pre-shared key reauthentication in 9 hours gcp[3]: IKE proposal: AES_GCM_16_256/PRF_HMAC_SHA2_512/MODP_2048 gcp{3}: INSTALLED, TUNNEL, reqid 1, ESP in UDP SPIs: c3f09701_i 4e8cc8d5_o gcp{3}: AES_GCM_16_256, 3438 bytes_i, 3135 bytes_o (49 pkts, 8s ago), rekeying in 2 hours gcp{3}: 0.0.0.0/0 === 0.0.0.0/0 # check that the BGP sessions works and the advertised routes are set sudo docker exec -it onprem_bird_1 ip route default via 10.0.16.1 dev eth0 10.0.0.0/24 proto bird src 10.0.16.2 nexthop via 169.254.1.1 dev vti0 weight 1 nexthop via 169.254.2.1 dev vti1 weight 1 10.0.16.0/24 dev eth0 proto kernel scope link src 10.0.16.2 10.10.0.0/24 proto bird src 10.0.16.2 nexthop via 169.254.1.1 dev vti0 weight 1 nexthop via 169.254.2.1 dev vti1 weight 1 35.199.192.0/19 proto bird src 10.0.16.2 nexthop via 169.254.1.1 dev vti0 weight 1 nexthop via 169.254.2.1 dev vti1 weight 1 169.254.1.0/30 dev vti0 proto kernel scope link src 169.254.1.2 169.254.2.0/30 dev vti1 proto kernel scope link src 169.254.2.2 199.36.153.4/30 proto bird src 10.0.16.2 nexthop via 169.254.1.1 dev vti0 weight 1 nexthop via 169.254.2.1 dev vti1 weight 1 199.36.153.8/30 proto bird src 10.0.16.2 nexthop via 169.254.1.1 dev vti0 weight 1 nexthop via 169.254.2.1 dev vti1 weight 1 # get a shell on the toolbox container sudo docker exec -it onprem_toolbox_1 sh # test pinging the IP address of the test instances (check outputs for it) ping 10.0.0.3 ping 10.10.0.3 # note: if you are able to ping the IP but the DNS tests below do not work, # refer to the sections above on configuring the DNS inbound fwd IP # test forwarding from CoreDNS via the Cloud DNS inbound policy dig test-1-1.gcp.example.org +short 10.0.0.3 dig test-2-1.gcp.example.org +short 10.10.0.3 # test that Private Access is configured correctly dig compute.googleapis.com +short private.googleapis.com. 199.36.153.8 199.36.153.9 199.36.153.10 199.36.153.11 # issue an API call via Private Access gcloud config set project [your project id] gcloud compute instances list ``` ### Cloud to onprem ```bash # connect to the test instance gcloud compute ssh test-1 # test forwarding from Cloud DNS to onprem CoreDNS (address may differ) dig gw.onprem.example.org +short 10.0.16.1 # test a request to the onprem web server curl www.onprem.example.org -s |grep h1
string
| ✓ | |
| [bgp_asn](variables.tf#L17) | BGP ASNs. | map(number)
| | {…}
|
| [bgp_interface_ranges](variables.tf#L28) | BGP interface IP CIDR ranges. | map(string)
| | {…}
|
| [dns_forwarder_address](variables.tf#L37) | Address of the DNS server used to forward queries from on-premises. | string
| | "10.0.0.2"
|
| [forwarder_address](variables.tf#L43) | GCP DNS inbound policy forwarder address. | string
| | "10.0.0.2"
|
| [ip_ranges](variables.tf#L49) | IP CIDR ranges. | map(string)
| | {…}
|
| [region](variables.tf#L64) | VPC region. | map(string)
| | {…}
|
| [ssh_source_ranges](variables.tf#L73) | IP CIDR ranges that will be allowed to connect via SSH to the onprem instance. | list(string)
| | ["0.0.0.0/0"]
|
## Outputs
| name | description | sensitive |
|---|---|:---:|
| [onprem-instance](outputs.tf#L17) | Onprem instance details. | |
| [test-instance1](outputs.tf#L26) | Test instance details. | |
| [test-instance2](outputs.tf#L33) | Test instance details. | |