Tag Archives: DNS

DNS

How To Use NSD, an Authoritative-Only DNS Server, on Ubuntu 14.04

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Introduction

Setting up a DNS server to be responsible for domain names can be a complex task even for seasoned administrators. DNS zone management is a vital duty, but can be bewildering, especially when attempting to get started.

Software like the Bind DNS server is incredibly flexible and can be configured to operate as many of the components in the overall DNS hierarchy. However, that flexibility also means that Bind is not optimized for any one task. This has a few side effects.

Most of the time there are huge chunks of functionality that your configuration has no need for. This additional complexity makes management more difficult. It also means that the software itself will be less responsive for any one task.

To solve this problem, alternative DNS servers have been created that specialize in a single area of DNS resolution. A piece of software known as NSD is an authoritative-only DNS server that is ideal for managing DNS zones authoritatively. Without the need to ever worry about recursion or caching, this server operates with high performance and a lower footprint.

In this guide, we will demonstrate how to install and configure NSD to securely administer our DNS zones on Ubuntu 14.04 servers. Continue reading How To Use NSD, an Authoritative-Only DNS Server, on Ubuntu 14.04 →

DNS

How To Configure BIND as a Private Network DNS Server on Ubuntu 14.04

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Introduction

An important part of managing server configuration and infrastructure includes maintaining an easy way to look up network interfaces and IP addresses by name, by setting up a proper Domain Name System (DNS). Using fully qualified domain names (FQDNs), instead of IP addresses, to specify network addresses eases the configuration of services and applications, and increases the maintainability of configuration files. Setting up your own DNS for your private network is a great way to improve the management of your servers.

In this tutorial, we will go over how to set up an internal DNS server, using the BIND name server software (BIND9) on Ubuntu 14.04, that can be used by your Virtual Private Servers (VPS) to resolve private host names and private IP addresses. This provides a central way to manage your internal hostnames and private IP addresses, which is indispensable when your environment expands to more than a few hosts.

The CentOS version of this tutorial can be found here.

Prerequisites

To complete this tutorial, you will need the following:

  • Some servers that are running in the same datacenter and have private networking enabled
  • A new VPS to serve as the Primary DNS server, ns1
  • Optional: A new VPS to serve as a Secondary DNS server, ns2
  • Root access to all of the above (steps 1-4 here)

If you are unfamiliar with DNS concepts, it is recommended that you read at least the first three parts of our Introduction to Managing DNS. Continue reading How To Configure BIND as a Private Network DNS Server on Ubuntu 14.04 →

DNS

How To Configure Bind as a Caching or Forwarding DNS Server on Ubuntu 14.04

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Introduction

DNS, or the Domain Name System, is often a difficult component to get right when learning how to configure websites and servers. While most people will probably choose to use the DNS servers provided by their hosting company or their domain registrar, there are some advantages to creating your own DNS servers.

In this guide, we will discuss how to install and configure the Bind9 DNS server as a caching or forwarding DNS server on Ubuntu 14.04 machines. These two configurations both have advantages when serving networks of machines.

Prerequisites and Goals

To complete this guide, you will first need to be familiar with some common DNS terminology. Check out this guide to learn about some of the concepts we will be implementing in this guide.

We will be demonstrating two separate configurations that accomplish similar goals: a caching and a forwarding DNS server.

To follow along, you will need to have access to two computers (at least one of which should be an Ubuntu 14.04 server). One will function as the client and the other will be configured as the DNS server. The details of our example configuration are:

Role IP Address
DNS Server 192.0.2.1
Client 192.0.2.100

We will show you how to configure the client machine to use the DNS server for queries. We will show you how to configure the DNS server in two different configurations, depending on your needs.

Caching DNS Server

The first configuration will be for a caching DNS server. This type of server is also known as a resolver because it handles recursive queries and generally can handle the grunt work of tracking down DNS data from other servers.

When a caching DNS server tracks down the answer to a client’s query, it returns the answer to the client. But it also stores the answer in its cache for the period of time allowed by the records’ TTL value. The cache can then be used as a source for subsequent requests in order to speed up the total round-trip time.

Almost all DNS servers that you might have in your network configuration will be caching DNS servers. These make up for the lack of adequate DNS resolver libraries implemented on most client machines. A caching DNS server is a good choice for many situations. If you do not wish to rely on your ISPs DNS or other publicly available DNS servers, making your own caching server is a good choice. If it is in close physical proximity to the client machines, it is also very likely to improve the DNS query times.

Forwarding DNS Server

The second configuration that we will be demonstrating is a forwarding DNS server. A forwarding DNS server will look almost identical to a caching server from a client’s perspective, but the mechanisms and work load are quite different.

A forwarding DNS server offers the same advantage of maintaining a cache to improve DNS resolution times for clients. However, it actually does none of the recursive querying itself. Instead, it forwards all requests to an outside resolving server and then caches the results to use for later queries.

This lets the forwarding server respond from its cache, while not requiring it to do all of the work of recursive queries. This allows the server to only make single requests (the forwarded client request) instead of having to go through the entire recursion routine. This may be an advantage in environments where external bandwidth transfer is costly, where your caching servers might need to be changed often, or when you wish to forward local queries to one server and external queries to another server.

Install Bind on the DNS Server

Regardless of which configuration choice you wish to use, the first step in implementing a Bind DNS server is to install the actual software.

The Bind software is available within Ubuntu’s default repositories, so we just need to update our local package index and install the software using apt. We will also include the documentation and some common utilities: Continue reading How To Configure Bind as a Caching or Forwarding DNS Server on Ubuntu 14.04 →

DNS

How To Set Up a Host Name with DigitalOcean

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DigitalOcean’s DNS allows you to easily set up your hostname from the DigitalOcean control panel.

Setup

Before you get started, you do need to have the following:

  • A Droplet (virtual private server) from DigitalOcean. If you don’t have one, you can register and set one up in under a minute
  • A Registered Domain Name. As of yet, you cannot register a domain through DigitalOcean.

Step One—Look Up Information with WHOIS

The first thing you need to do to set up your host name is to change your domain name server to point to the DigitalOcean name servers. You can do this through your domain registrar’s website. If you do not remember where you registered your name, you can look it up using “WHOIS”, a protocol that displays a site’s identifying information, such as the IP address and registration details.

Open up the command line and type: Continue reading How To Set Up a Host Name with DigitalOcean →

DNS

A Comparison of DNS Server Types: How To Choose the Right DNS Configuration

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Introduction

DNS, or the Domain Name System, is an integral part of how systems connect with each other to communicate on the internet. Without DNS, computers, and the people who use them, would be required to connect using only numerical addresses known as IP addresses.

Besides the obvious problem of having to remember a large number of complex numbers for simple tasks, communicating through IP addresses also causes some additional problems. Moving your website to a different hosting provider, or moving your servers to different locations would require you to inform every client of the new location.

DNS servers, the computers that together form the system that allow us to use names instead of addresses, can server many different functions, each of which can contribute to your ability to accessing servers by name.

In a previous guide we discussed some of the basic terminology and concepts of the domain name system. We will assume some familiarity with the concepts covered in that article. In this guide, we will talk about some of the different types of DNS server setups and what the advantages, use cases, and properties are of each. Continue reading A Comparison of DNS Server Types: How To Choose the Right DNS Configuration →

DNS

An Introduction to DNS Terminology, Components, and Concepts

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Introduction

DNS, or the Domain Name System, is often a very difficult part of learning how to configure websites and servers. Understanding how DNS works will help you diagnose problems with configuring access to your websites and will allow you to broaden your understanding of what’s going on behind the scenes.

In this guide, we will discuss some fundamental DNS concepts that will help you hit the ground running with your DNS configuration. After tackling this guide, you should be ready to set up your domain name with DigitalOcean or set up your very own DNS server.

Before we jump into setting up your own servers to resolve your domain or setting up our domains in the control panel, let’s go over some basic concepts about how all of this actually works.

Domain Terminology

We should start by defining our terms. While some of these topics are familiar from other contexts, there are many terms used when talking about domain names and DNS that aren’t used too often in other areas of computing.

Let’s start easy: Continue reading An Introduction to DNS Terminology, Components, and Concepts →

Linux

Building for Production: Web Applications — Recovery Planning

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Building for Production: Web Applications — Recovery Planning

Introduction

Now that we have our example application setup, we should devise a recovery plan. A recovery plan is a set of documented procedures to recover from potential failures or administration errors within your server setup. Creating a recovery plan will also help you identify the essential components and data of your application server setup.

A very basic recovery plan for a server failure could consist of the list of steps that you took to perform your initial server deployment, with extra procedures for restoring application data from backups. A better recovery plan might, in addition to good documentation, leverage deployment scripts and configuration management tools, such as Ansible, Chef, or Puppet, to help automate and quicken the recovery process.

Recovery Plan Diagram

In this part of the tutorial, we will demonstrate how to create a basic recovery plan for the example WordPress application that we set up. Your needs will probably differ, but this should help you get started with devising a recovery plan of your own.

Recovery Plan Requirements

Our basic requirements are that we are able to recover from the loss of any server in the setup, and restore the application functionality and data (up to a reasonable point in time). To fulfill this goal, we will create an inventory of each server, determine which data needs to be backed up, and write a recovery plan based on our available assets. Of course, if any of these recovery plans are executed, the application should be tested to verify that it was restored properly. Continue reading Building for Production: Web Applications — Recovery Planning →

Linux

Building for Production: Web Applications — Deploying

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Building for Production: Web Applications — Deploying
Introduction

In this part of the tutorial, we will deploy our example PHP application, WordPress, and a private DNS:

DNS + Application Diagram

Your users will access your application over HTTPS via a domain name, e.g. “https://www.example.com”, that points to the load balancer. The load balancer will act as a reverse proxy to the application servers, which will connect to the database server. The private DNS will enable us to use names to refer to the private network addresses of our servers which ease the process of configuration of our servers.

We will set up the components that we just discussed on six servers, in this order:

  • Private DNS (ns1 and ns2)
  • Database Server (db1)
  • Application Servers (app1 and app2)
  • Load Balancer (lb1)

Let’s get started with the DNS setup.

Private DNS Servers

Using names for addresses helps with identifying the servers you are working with and becomes essential for the maintenance of a larger server setup, as you can replace a server by simply updating your DNS records (in a single place) instead of updating countless configuration files with IP addresses. In our setup, we will set up our DNS so we can reference the private network addresses of our servers by name instead of IP address.

We will refer to the private network address of each server by a hostname under the “nyc3.example.com” subdomain. For example, the database server’s private network address would be “db1.nyc3.example.com”, which resolves to it’s private IP address. Note that the example subdomain is almost completely arbitrary, and is usually chosen based on logical organization purposes; in our case, we “nyc3” indicates that the servers are in the NYC3 datacenter, and “example.com” is our application’s domain name.

Set this up by following this tutorial, and adding DNS records for each server in your setup:

After completing the DNS tutorial, you should have two BIND servers: ns1 and ns2. If you already know the private IP addresses of all of the servers in your setup, add them to your DNS now; otherwise, add the appropriate DNS records as you create your servers.

Now we’re ready to set up our database server.

Set Up Database Server

Because we want to load balance the our application servers, i.e. the ones running Apache and PHP, we need to decouple the database from the application servers by setting it up on a separate server. Decoupling the database from the application is an essential step before horizontally scaling many types of applications, as explained in this blog post: Horizontally Scaling PHP Applications: A Practical Overview.
Continue reading Building for Production: Web Applications — Deploying →

Linux

Building for Production: Web Applications — Overview

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Building for Production: Web Applications — Overview

Introduction

This 6-part tutorial will show you how to build out a multi-server production application setup from scratch. The final setup will be supported by backups, monitoring, and centralized logging systems, which will help you ensure that you will be able to detect problems and recover from them. The ultimate goal of this series is to build on standalone system administration concepts, and introduce you to some of the practical considerations of creating a production server setup.

If you are interested in reviewing some of the concepts that will be covered in this series, read these tutorials:

While the linked articles provide general guidelines of a production application setup, this series will demonstrate how to plan and set up a sample application from start to finish. Hopefully, this will help you plan and implement your own production server environment, even if you are running a different application on a completely different technology stack. Because this tutorial covers many different system administration topics, it will often defer the detailed explanation to external supporting articles that provide supplemental information.

Our Goal

By the end of this set of tutorials, we will have a production server setup for a PHP application, WordPress for demonstration purposes, that is accessible via https://www.example.com/. We will also include servers that will support the production application servers. The final setup will look something like this (private DNS and remote backups not pictured):

Production Setup

In this setup, the servers in the Application box are considered to be essential for the application run properly. Aside from the recovery plan and the remote backup server, the remaining components—backups, monitoring, and logging—will be added to support the production application setup. Each component will be installed on a separate Ubuntu 14.04 server within the same DigitalOcean region, NYC3 in our example, with Private Networking enabled.

Continue reading Building for Production: Web Applications — Overview →