DNS plays the ‘phone book’ role in the internet world. As multi-cloud setup has become more and more prevalent for enterprise customers. The Integration of customer-owned on-premise networks with cloud-based infrastructures to provide a seamless domain name resolution experience is vital to customers’ enterprise landscapes.
In this article, we are addressing such scenarios, where SAP RISE PCE customers have their SAP workloads hosted on SAP managed cloud environment (on Azure, AWS, GCP, or SAP Data Center), while might also have one or both of: their own on-premise data centers, and their own hyperscalers (Azure, AWS, or GCP) subscription. And each network environment has its own DNS setup. Chaos might occur if domain names or IP ranges were not properly routed.
Thereby, we are proposing a reference architecture for such scenarios to resolve DNS requests coming from all sources (SAP RISE PCE managed environments, on-premise data center DNS servers, and customer’s own hyperscalers DNS services), with disaster recovery been considered.
Terminologies and Abbraviations
DNS: short for Domain Name System. It translates between domain names (like *.ecs.sap.com) and IP addresses (like 192.168.1.1 in IPv4, 2400:cb00:2048:1::c629:d7a2 in IPv6) in both ways.
DNS Zone Transfer: [SAP RISE PCE preferred] one of the mechanisms to replicate DNS databases across a set of DNS servers. SAP RISE PCE recommends this because of: its high availability; it provides redundancy and higher SLA, especially for DR scenarios; it can establish reliable status monitoring. The disadvantage is: DNS Notifiers should be in place to ensure the full DNS TTL Delay.
DNS Conditional Forward (or so-called ‘IP Forward’): DNS servers that only forward queries for specific domain names. The advantage is, if no outbound traffic from SAP RISE PCE is necessary, customers do not have to configure their own DNS for their inbound traffic. The disadvantages are: customer OP DNS may suffer delay due to forward cache (but configurable); also due to forward cache, failover could take more time; limited status monitoring.
Zone Delegation: a process of assigning authority over a domain or subdomain to different DNS servers to keep records updated. The advantage is: customers can manage OP DNS through SAP RISE PCE as a single point. The disadvantages are: configuration is onerous.
Consensus / Prerequisites
Only server-side DNS servers are been considered in this reference architecture, client-side DNS (if any) are not been addressed here
Disaster recovery on customer’s data center is not been considered
Network connections for pairing virtual networks or connecting on-premise networks with the cloud (like VPC peering, VNet peering, VPN, .etc), and other network components (like load balancer, .etc.) are not been addressed in this reference architecture. Separate reference architectures will be created in later blog series.
SAP RISE PCE DNS servers are seen as resources.
DNS services on customer’s own hyperscalers are seen as services, and customers should ensure HA/DR been enabled on service level
In DR cases, we call it by zone, instead of region, since RISE customers can may deploy SDDR (different zones within the same region), or LDDR (in different regions)
In SDDR, a virtualized DNS server deployed within each zone. In LDDR, a virtualized DNS server cluster (contains 2 DNS servers for HA) deployed within each zone. There are SAP tools doing syncronization in between DNS servers (clusters).
The offerings by hyperscalers (Azure, AWS, and GCP) are based on the services’ general availability of hyperscalers providers’ (Microsoft, Amazon, and Google) official documentation online, as of this blog’s publishing date of time The offerings by SAP RISE PCE are based on SAP ECS service guidance as of this blog’s publishing date of time
customer’s AWS subscription
DNS zone transfer
(RISE PCE preferred)
AWS DNS is a server (cluster) deployed on AWS EC2 (see Fig. 1 and Fig. 2)
DNS conditional forward
Route53 resolver based on Route53 is used to integrate DNS from another peered VPC (eg. RISE DNS on SAP-managed AWS VPC), OP network that is connected to AWS with AWS Direct Connect, a VPN, or a network address translation (NAT) gateway. See Fig. 3 and Fig. 4.