Added details about DNS setup

docs/architecture-and-infrastructure/index.md

@@ -2,6 +2,6 @@
 
 In order to run the service we have to have resource for data processing and supporting our applications/apis. This section focusses on laying out the architecture behind the infrastructure and what infrastructure is deployed.
 
-* [Solution design](/architecture-and-infrastructure/solution-design/) - uses c4 diagrams to lay out the architecture for our system and it's components
+* [Solution design](/architecture-and-infrastructure/solution-design/) - uses C4 diagrams to lay out the architecture for our system and it's components
 * [Architecture Decision Records (ADRs)](/architecture-and-infrastructure/architecture-decision-records/) - A list of decisions we have taken whille building this system.
 * [Design Proposals (DPs)](/architecture-and-infrastructure/proposals/) - significant proposals for changes to our solution design. 

docs/architecture-and-infrastructure/solution-design/dns.md

@@ -0,0 +1,28 @@
+# Solution design - DNS
+
+## Overview
+
+The Domain Name System (DNS) setup for the planning data service involves the delegation of the planning subdomain from![img.png](img.png) the data.gov.uk domain which is managed by GDS (Government Digitial Service).  A name server lookup for the planning name server record reveals the following:
+
+```shell
+$ nslookup -q=ns planning.data.gov.uk
+Server:		fe80::d686:60ff:fe40:eb3d%15
+Address:	fe80::d686:60ff:fe40:eb3d%15#53
+
+Non-authoritative answer:
+planning.data.gov.uk	nameserver = ns-519.awsdns-00.net.
+planning.data.gov.uk	nameserver = ns-1995.awsdns-57.co.uk.
+planning.data.gov.uk	nameserver = ns-79.awsdns-09.com.
+planning.data.gov.uk	nameserver = ns-1442.awsdns-52.org.
+```
+
+The four nameserver records returned refer to the planning.data.gov.uk Route 53 zone in our production AWS account.  From that zone, further delegations have been made for our non-production environments:
+
+ * staging.planning.data.gov.uk
+ * development.planning.data.gov.uk
+
+The delegations correspond to the Route 53 zones in the staging and development AWS accounts.
+
+## DNS Delegation Diagram
+
+![DNS Delegation](/images/dns.drawio.png)

docs/architecture-and-infrastructure/solution-design/index.md

@@ -12,4 +12,9 @@ The solution architecture for the Planning Data Service has been modelled using
 
  * [Data Pipelines](/architecture-and-infrastructure/solution-design/data-pipelines/)
  * [Planning Data Platform](/architecture-and-infrastructure/solution-design/planning-data-platform/)
- * [Check service](/architecture-and-infrastructure/solution-design/check-service/)
+ * [Check service](/architecture-and-infrastructure/solution-design/check-service/)
+
+
+### Others
+
+ * [DNS Setup](/architecture-and-infrastructure/dns/)