Have you ever wondered how your web browser finds a website when you type in a domain name? DNS records play a crucial role in the functioning of the internet. We will delve into the specifics of DNS records and their significance in resolving domain names to IP addresses. DNS records in a DevOps role ensure smooth operations, efficient application deployment, and reliable service delivery.
DNS? I've heard that before...
DNS stands for Domain Name System. Its fundamental job is to convert user-friendly domain names (like example.com) into machine-readable IP addresses (like 192.0.2.1). Computers communicate using IP addresses, but humans find it easier to remember domain names. DNS acts as a directory service that allows seamless communication between humans and machines on the internet.
The DNS Hierarchy and Server Levels
The DNS hierarchy consists of three primary levels of servers: the Root Servers, the Top-Level Domain (TLD) Servers, and the Authoritative Name Servers. Among these, authoritative name servers are responsible for storing DNS records. But for the query to reach the correct corresponding Authoritative Name Server, it has to go through the other two. Root Server forwards the query to the correct Top-Level Domain Server, which contains information about all the Top-Level Domains. The TLD of example.com is .com. This server identifies which ANS to direct the query to.
This process of forwarding your query may or may not require you to connect to the internet, but in each case, you would need a DNS resolver to intercept your query after each redirection in case it has it stored in the local DNS server's local cache. When the DNS resolver returns your query immediately, i.e., without making any further queries, they are called 'Non-recursive' queries. When it does, recursive queries. The first query is 'recursive' when a DNS lookup is initiated. However, sometimes the resolver has to request the Root Server because the query results are not cached. These queries are 'iterative.'
DNS records
Usually, DNS records have the following fields -
- Type: Specifies the type of domain resolution
- Name: Name of the domain
- IP Address
- Alias To: Stores aliases for domain names
- TTL (Time To Live): The time duration for which the record is valid until the next update.
A record
The A record (Address record) is the most common DNS record. It maps a domain name to a specific IPv4 address.
AAAA record
AAAA record (Quad A record) performs a similar function but maps domain names to IPv6 addresses, the newer 128-bit alphanumeric addresses.
CNAME Records
Your domain (say www.example.com) has several parts:
- Root Domain
- Top Level Domain
- 2nd Level Domain
- Subdomain
In the example domain, the Root Domain is hidden, The Top-Level Domain is '.com,' the 2nd level domain is 'example,' and if there was an additional name to the left of 'example,' it would be a subdomain. The most common subdomain is 'www.'
The CNAME (Canonical Name) record is an alias for another domain name. It resolves a domain or subdomain, via its 'Alias To' field, to the canonical representation of another domain. This record helps manage subdomains and direct traffic to the correct location.
MX Records
MX (Mail Exchanger) records are essential for handling email services. They point to the servers responsible for receiving and processing email messages for a specific domain name. MX records are crucial for proper email delivery and spam prevention.
SOA Records
The SOA (Start of Authority) document contains administrative information about a DNS zone. A DNS zone is a section of a domain name space that an administrator has control over. SOA records are used for versioning and synchronizing data across secondary DNS servers.
NS Records
NS (Name Server) records provide the names of authoritative name servers within a domain. These servers hold all the necessary DNS records for resolving queries related to the domain. NS records typically include primary and secondary name servers.
SRV Records
The SRV (Service) record points to a server and specifies a specific service associated with that server, along with the port number. Applications like VoIP and instant messaging use SRV records to find the location of the desired service.
PTR Records
PTR (Pointer) records perform the reverse of A and AAAA records. They resolve IP addresses back to domain names. These records validate email senders and prevent spam through reverse DNS lookup.
TXT Records
The TXT (Text) record contains miscellaneous information about a domain. It can include general or contact information and is often used to verify the authenticity of email senders.
How is this related to DevOps?
A DevOps engineer ensures seamless app deployment, load balancing, high availability, and disaster recovery. Understanding DNS records enables secure email communication, network security, and access control. It is vital for infrastructure monitoring, domain migration, and managing microservices.
A wide range of uses from running a DNS lookup for deployment to analyzing DNS logs and records to gain insights into the patterns of traffic accessing different domain names to tracking DNS resolution times to identify latency issues.