Designing the Namespace Structure

Designing the NIS+ namespace is one of the most important tasks you can perform, since changing the domain structure after NIS+ has been set up is a time-consuming, complex job. It is complex because information, security, and administration policies are woven into the domain structure of the namespace. Rearranging domains requires rearranging information, reestablishing security, and recreating administration policies.

When designing the structure of an NIS+ namespace, consider the factors which are discussed in the following sections of this chapter:

Domain Hierarchy

The main benefit of an NIS+ domain hierarchy is that it allows the namespace to be divided into more easily managed components. Each component can have its own security, information management, and administration policies. It is advisable to have a hierarchy when the number of clients you have exceeds 500, if you want to set up different security policies for a set of users, or if you have geographically distributed sites.

Unless there is a need for a domain hierarchy, not having a hierarchy can simplify your transition to NIS+. When all users were in the same NIS domain, they were directly visible to each other without using fully qualified names. Creating an NIS+ hierarchy, however, puts users in separate domains, which means that the users in one domain are not directly visible to users in another domain, unless you use fully qualified names or paths.

For example, if there are two subdomains, sales.com. and factory.com., created out of the earlier .com. domain, then for user juan in the sales.com. domain to be able to send mail to user myoko in factory.com., he would have to specify her name as myoko@hostname.factory.com. (or myoko@hostname.factory) instead of just myoko, as was sufficient when they were in the same domain. Remote logins also require fully qualified names between domains.

You could use the table path to set up connections between tables in one domain and another domain, but to do so would negate the advantages of having a domain hierarchy. You would also be reducing the reliability of the NIS+ service because now clients would have to depend upon the availability of not only their own home domains, but also of other domains to which their tables are pathed. Using table paths may also slow request response time.

Domain Hierarchy – Solaris 2.6 and Earlier

In Solaris 2.6 and earlier, the NIS+ servers for each subdomain are not part of the subdomain that they serve, with the exception of the root domain. The NIS+ servers are in the parent domain of the subdomain they serve. This relationship of server to subdomain creates problems for applications that expect the servers to be able to get their name-service data from the subdomain. For example, if a subdomain NIS+ server is also an NFS server, then the server does not get its netgroups information from the subdomain; instead, it retrieves the information from its domain, which is the domain above the subdomain; this can be confusing. Another example of when a hierarchy can cause problems is where the NIS+ server is also used by users to log in remotely and to execute certain commands that they cannot execute from their own machines. If you have only a single root domain, you do not have these problems because NIS+ root servers live in the domain that they serve.

Domain Hierarchy – Solaris 9

In the Solaris operating environment, the NIS+ server for a domain can be in the same domain it serves. This allows a server to set its domain name to the same as that used by its clients without affecting the server's ability to securely communicate with the rest of the domain hierarchy.

Designing a Domain Hierarchy

If you are unfamiliar with domain hierarchies, first read Chapter 2, NIS+: An Introduction. It describes NIS+ domain structure, information storage, and security.

After you are familiar with the components of a domain hierarchy, make a diagram of how you expect the hierarchy to look when you are finished. The diagram will be a useful reference when you are in the midst of the setup procedure. At a minimum, you will need to consider the following issues:

• Organizational or geographical mapping

• Connection to higher domain.

• Client support in the root domain.

• Domain size compared to number of domains.

• Number of levels.

• Security levels.

• Replicas and number of replicas.

• Information management.

Remember that a domain is not an object, but a reference to a collection of objects. Therefore, a server that supports a domain is not actually associated with the domain but with the domain's directories. A domain consists of four directories: domain, ctx_dir.domain, org_dir.domain, and groups_dir.domain, as shown below.

Figure 26–3 Server Relationship to Domain

Organizational or Geographical Mapping

One of the major benefits of NIS+ is its capability of dividing the namespace into smaller, more manageable parts. You could create a hierarchy of organizations, such as those of the hypothetical corporation, Doc Inc., as shown below.

Figure 26–4 Sample NIS+ Hierarchy by Logical Organization

You could also organize the hierarchy by buildings instead of organizations, as shown below.

Figure 26–5 Sample NIS+ Hierarchy by Physical Location

The scheme you select depends primarily on how you prefer to administer the namespace and how clients will tend to use the namespace. For example, if clients of factory.com. will be distributed throughout the buildings of Doc Inc., you should not organize the namespace by building. Because the clients constantly need to have access to other domains, you need to add their credentials to the other domains and you increase traffic flow through the root master server. A better scheme would be to arrange clients by organization. On the other hand, building-sized domains are immune to the reorganizations that require organization-based domains to be restructured.

Do not be limited by the physical layout of the network; an NIS+ namespace does not have to be congruent with the physical network, except where it has to support NIS clients. The number of domains your namespace needs depends on the kind of hierarchy you select.

Consider future expansion plans. Will today's NIS+ root domain be beneath another NIS+ domain in the future? Changing this arrangement would entail a great deal of work. Try to estimate the need for future domains in the namespace and design a structure that can accommodate them without disruption.

Connection to Higher Domains?

Consider whether the NIS+ namespace will be connected to higher domains, such as those of the Internet or DNS. If you currently use NIS under a DNS hierarchy, do you want to replace only the NIS domains or do you want to replace the entire company-wide DNS/NIS structure with an NIS+ namespace?

Client Support in the Root Domain

In the two Doc Inc., domain hierarchies illustrated in Figure 26–4 and Figure 26–5, are all the clients placed in domains beneath the root domain? Or do some belong to the root domain? Is the purpose of the root domain to act only as the root for its subdomains, or will it support its own group of clients? You could place all clients in the lowest layer of domains, and only those used for administration in the root and any intermediate domains. For example, if you implemented the plan in Figure 26–4, all clients would belong to the big.sales.com., small.sales.com., and factory.com. domains, and only clients used for administration would belong to the .com. and sales.com. domains.

Or you could place the clients of general-purpose departments in higher-level domains. For example, in Figure 26–5, where the domain is organized by building, you could put the clients of the Facilities Department in the .com. domain. It is not recommended that you do so, however, because the root domain should be kept simple and relatively unpopulated.

Domain Size Compared With Number of Domains

The current NIS+ implementation is optimized for up to 1000 NIS+ clients per domain and for up to 10 replicas per domain. Such a domain would typically have 10,000 table entries. The limitations come from the current server discovery protocol. If you have more than 1000 NIS+ clients, you should divide your namespace into different domains and create a hierarchy.

Creating a hierarchy, however, may introduce more complexity than you are prepared to handle. You may still prefer to create larger domains rather than a hierarchy; because one large domain requires less administration than multiple smaller domains. Larger domains need fewer skilled administrators to service them, since tasks can be automated more readily (with scripts you create), thus lowering the administrative expense. Smaller domains provide better performance, and you can customize their tables more easily. You also achieve greater administrative flexibility with smaller domains.

Number of Levels

NIS+ was designed to handle multiple levels of domains. Although the software can accommodate almost any number of levels, a hierarchy with too many levels is difficult to administer. For example, the names of objects can become long and unwieldy. Consider 20 to be the limit for the number of subdomains for any one domain and limit the levels of the NIS+ hierarchy to 5.

Security Level

Typically, you will run the namespace at security level 2. However, if you plan to use different security levels for different domains, you should identify them now. Understanding the Impact of NIS+ Security provides more information about security levels.

Domains Across Time Zones

Geographically-dispersed organizations may determine that organizing their domain hierarchy by functional groups causes a domain to span more than one time zone. It is strongly recommended that you do not have domains that span multiple time zones. If you do need to configure a domain across time zones, be aware that a replica's time is taken from the master server, so the database updates will be synchronized properly, using Greenwich mean time (GMT). This may cause problems if the replica machine is used for other services that are time critical. To make domains across time zones work, the replica's /etc/TIMEZONE file has to be set locally to the master server's time zone when you are installing NIS+. After the replica is running, some time-critical programs may run properly and some may not, depending on whether these programs use universal or local time.

Information Management

It is best to use a model of local administration within centralized constraints for managing the information in an NIS+ namespace. Information should be managed, as much as possible, from within its home domain, but according to guidelines or policies set at the global namespace level. This provides the greatest degree of domain independence while maintaining consistency across domains.

Domain Names

Consider name length and complexity. First, choose names that are descriptive. For example, “Sales” is considerably more descriptive than “BW23A.” Second, choose short names. To make your administrative work easier, avoid long names such as administration_services.corporate_headquarters.doc.com.

A domain name is formed from left to right, starting with the local domain and ending with the root domain. The root domain must always have at least two labels and must end in a dot. The second label can be an Internet domain name, such as “com.”

Also consider implications of particular names for email domains, both within the company and over the Internet.

Depending on the migration strategy, a viable alternative is to change domain names on NIS to the desired structure, then migrate to NIS+ domain by domain.

Email Environment

Because NIS+ can have a domain hierarchy while NIS has a flat domain space, changing to NIS+ can have effects on your mail environment. With NIS, only one mail host is required. If you use a domain hierarchy for NIS+, you may need one mail host for each domain in the namespace because names in separate domains may be no longer unique.

Therefore, the email addresses of clients who are not in the root domain may change. As a general rule, client email addresses can change when domain names change or when new levels are added to the hierarchy.

In earlier Solaris releases, these changes required a great deal of work. This release provided several sendmail enhancements to make the task easier. In addition, NIS+ provides a sendmailvars table. The sendmail program first looks at the sendmailvars table (see Figure 26–7, then examines the local sendmail.cf file.

Be sure that mail servers reside in the NIS+ domain whose clients they support. For performance reasons, do not use paths to direct mail servers to tables in other domains.

Consider the impact of the new mail addresses on DNS. You may need to adjust the DNS MX records.