Mapping IP addresses
1. Mapping IP addresses
Regardless of whether you use an ephemeral or static IP address, the external address is unknown to the OS of the VM. The external IP address is mapped to the VM's internal address transparently by VPC. I am illustrating this here by running ifconfig within a VM in Google Cloud, which only returns the internal IP address. Let's explore this further by looking at DNS resolution for both internal and external addresses. Let's start with internal addresses. Google Cloud has two types of internal DNS names, Zonal and Global (project wide) DNS. In general, Google strongly recommends using zonal DNS because it offers higher reliability guarantees by isolating failures in the DNS registration to individual zones. Each instance has a hostname that can be resolved to an internal IP address. This hostname is the same as the instance name. There is also an internal fully qualified domain name for an instance that uses the format shown on the slide. If you delete and recreate an instance, the internal IP address can change. This change can disrupt connections from other Compute Engine resources, which must obtain the new IP address before they can connect again. However, the DNS name always points to a specific instance, no matter what the internal IP address is. Each instance has a metadata server that also acts as a DNS resolver for that instance. The metadata server handles all DNS queries for local network resources and routes all other queries to Google's public DNS servers for public name resolution. I previously mentioned that an instance is not aware of any external IP address assigned to it. Instead, the network stores a lookup table that matches external IP addresses with the internal IP addresses of the relevant instances. Now, let's look at external addresses. Instances with external IP addresses can allow connections from hosts outside of the project. Users can do so directly using the external IP address. Public DNS records pointing to instances are not published automatically; however, admins can publish these using existing DNS servers. Domain name servers can be hosted on Google Cloud, using Cloud DNS. This is a managed service that is definitely worth considering, so let's explore it in more detail. Cloud DNS is a scalable, reliable, and managed authoritative Domain Name System, or DNS, service running on the same infrastructure as Google. Cloud DNS translates requests for domain names like google.com into IP addresses. Cloud DNS uses Google's global network of Anycast name servers to serve your DNS zones from redundant locations around the world, providing lower latency and high availability for your users. High availability is very important because if you can't look up a domain name, the internet might as well be down. That's why Google Cloud offers a 100% uptime Service Level Agreement, or SLA, for domains configured in Cloud DNS. Cloud DNS lets you create and update millions of DNS records without the burden of managing your own DNS servers and software. Instead, you use a simple user interface, command-line interface, or API. Another networking feature of Google Cloud is Alias IP Ranges. Alias IP Ranges let you assign a range of internal IP addresses as an alias to a virtual machine's network interface. This is useful if you have multiple services running on a VM, and you want to assign a different IP address to each service. In essence, you can configure multiple IP addresses, representing containers or applications hosted in a VM, without having to define a separate network interface. You just draw the alias IP range from the local subnet's primary or secondary CIDR ranges. This diagram provides a basic illustration of primary and secondary CIDR ranges and VM alias IP ranges.2. Let's practice!
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