docs: Reuse VCN (#524)

* docs: Reuse VCN

* docs: Updated for Reuse VCN

Author: karthicgit

docs/reusevcn.adoc

@@ -0,0 +1,30 @@
+= Reuse VCN
+:idprefix:
+:idseparator:
+:sectlinks:
+:sectnums:
+:toc: auto
+
+:uri-repo: https://github.com/oracle-terraform-modules/terraform-oci-oke
+
+:uri-rel-file-base: link:{uri-repo}/blob/main
+:uri-rel-tree-base: link:{uri-repo}/tree/main
+
+:uri-docs-reuse-vcn: {uri-rel-file-base}/docs/terraformoptions.adoc#reuse-vcn
+
+:uri-ig-docs: https://docs.oracle.com/en-us/iaas/Content/Network/Tasks/managingIGs.htm
+
+:uri-nat-docs: https://docs.oracle.com/en-us/iaas/Content/Network/Tasks/NATgateway.htm
+
+
+== Assumptions
+Internet Gateway, NAT Gateway,Service Gateway was created in the VCN and route table preexist.
+
+== Instructions
+By default the module will create VCN ,gateways etc and then create Oracle kubernetes engine cluster. There are usecases where enduser might want to reuse their existing VCN . To do that set `create_vcn = false` and pass other required values mentioned in {uri-docs-reuse-vcn}[terraformoptions] under Reuse VCN section.
+
+You can pass either the vcn_display_name or vcn_id .Recommended to use vcn_id as vcn_display name can have duplicate value. If both values are passed vcn_id will take precedence. Similarly for Internet Gateway and NAT Gateway route table you can either pass displayname(`ig_route_table_display_name` and `nat_route_table_display_name`) or pass the id (`ig_route_table_id` and `nat_route_table_id`) . 
+
+The internet gateway route table should have a minimum route with destination CIDR  `0.0.0.0/0` and target as `Internet Gateway` . For more details please refer {uri-ig-docs}[Internet Gateway]
+
+The NAT gateway route table should have a minimum route with destination CIDR to `0.0.0.0\0` or specific CIDR as per your network requirement and target as `NAT Gateway`. For more details please refer {uri-nat-docs}[NAT Gateway]

docs/terraformoptions.adoc

@@ -250,6 +250,51 @@ EOT
 |
 |oke-vcn
 
+|===
+== Reuse VCN
+
+[stripes=odd,cols="1m,4d,2m,2m", options=header,width="100%"]
+|===
+|Parameter
+|Description
+|Values
+|Default
+
+|create_vcn
+|Whether to create the VCN.
+|true/false
+|true
+
+|vcn_display_name
+|Existing VCN display name where the resources will be created.
+|
+|
+
+|vcn_id
+|Existing VCN OCID where the resources will be created
+|
+|
+
+|ig_route_table_display_name
+|Existing Internet Gateway route table display name
+|
+|
+
+|ig_route_table_id 
+|Existing Internet Gateway route table OCID
+|
+|
+
+|nat_route_table_display_name
+|Existing NAT Gateway route table OCID
+|
+|
+
+|nat_route_table_id
+|Existing NAT Gateway route table OCID
+|
+|
+
 |===
 
 == Bastion Host