When we are talking about server systems, networking is the first and most important factor. If you are using an Ubuntu server in a cloud or virtual machine, you generally don't notice the network settings, as they are already configured with various network protocols. However, as your infrastructure grows, managing and securing the network becomes the priority.

Networking can be thought of as an umbrella term for various activities that include network configurations, file sharing and network time management, firewall settings and network proxies, and many others. In this chapter, we will take a closer look at the various networking services that help us set up and effectively manage our networks, be it in the cloud or a local network in your office.

When you install Ubuntu server, its network setting defaults to dynamic IP addressing, that is, the network management daemon in Ubuntu searches for a DHCP server on the connected network and configures the network with the IP address assigned by DHCP. Even when you start an instance in the cloud, the network is configured with dynamic addressing using the DHCP server setup by the cloud service provider. In this chapter, you will learn how to configure the network interface with static IP assignment.

DHCP is a service used to automatically assign network configuration to client systems. DHCP can be used as a handy tool when you have a large pool of systems that needs to be configured for network settings. Plus, when you need to change the network configuration, say to update a DNS server, all you need to do is update the DHCP server and all the connected hosts will be reconfigured with new settings. Also, you get reliable IP address configuration that minimizes configuration errors and address conflicts. You can easily add a new host to the network without spending time on network planning.

DHCP is most commonly used to provide IP configuration settings, such as IP address, net mask, default gateway, and DNS servers. However, it can also be set to configure the time server and hostname on the client.

DHCP can be configured to use the following configuration methods:

DNS, also known as name server, is a service on the Internet that provides mapping between IP addresses and domain names and vice versa. DNS maintains a database of names and related IP addresses. When an application queries with a domain name, DNS responds with a mapped IP address. Applications can also ask for a domain name by providing an IP address.

DNS is quite a big topic, and an entire chapter can be written just on the DNS setup. This recipe assumes some basic understanding of the working of the DNS protocol. We will cover the installation of BIND, installation of DNS server application, configuration of BIND as a caching DNS, and setup of Primary Master and Secondary Master. We will also cover some best practices to secure your DNS server.

In this recipe, we will install and configure the squid proxy and caching server. The term proxy is generally combined with two different terms: one is forward proxy and the other is reverse proxy.

When we say proxy, it generally refers to forward proxy. A forward proxy acts as a gateway between a client's browser and the Internet, requesting the content on behalf of the client. This protects intranet clients by exposing the proxy as the only requester. A proxy can also be used as a filtering agent, imposing organizational policies. As all Internet requests go through the proxy server, the proxy can cache the response and return cached content when a similar request is found, thus saving bandwidth and time.

A reverse proxy is the exact opposite of a forward proxy. It protects internal servers from the outside world. A reverse proxy accepts requests from external clients and routes them to servers behind the proxy. External clients can see a single entity...

Network Time Protocol (NTP) is a TCP/IP protocol for synchronizing time over a network. Although Ubuntu has a built-in clock that is helpful for keeping track of local events, it may create issues when the server is connected over a network and provides time-critical services to the clients. This problem can be solved with the help of NTP time synchronization. NTP works by synchronizing time across all servers on the Internet.

NTP uses hierarchies of servers with top-level servers synchronizing time with atomic clocks. This hierarchy levels are known as stratum, and the level can range between 1 and 15, both inclusive. The highest stratum level is 1 and is determined by the accuracy of the clock the server synchronizes with. If a server synchronizes with other NTP server with stratum level 3, then the stratum level for this server is automatically set to 4.

Another time synchronization tool provided by Ubuntu is ntpdate, which comes preinstalled with Ubuntu. It executes...

When an application becomes popular, it sends an increased number of requests to the application server. A single application server may not be able to handle the entire load alone. We can always scale up the underlying hardware, that is, add more memory and more powerful CUPs to increase the server capacity; but these improvements do not always scale linearly. To solve this problem, multiple replicas of the application server are created and the load is distributed among these replicas. Load balancing can be implemented at OSI Layer 4, that is, at TCP or UDP protocol levels, or at Layer 7, that is, application level with HTTP, SMTP, and DNS protocols.

In this recipe, we will install a popular load balancing or load distributing service, HAProxy. HAProxy receives all the requests from clients and directs them to the actual application server for processing. Application server directly returns the final results to the client. We will be setting HAProxy...