YARN-5244. Documentation required for DNS Server implementation. Contributed by Jon Maron

hadoop-project/src/site/site.xml

@@ -155,6 +155,11 @@
       <item name="Timeline Service V.2" href="hadoop-yarn/hadoop-yarn-site/TimelineServiceV2.html#Timeline_Service_v.2_REST_API"/>
     </menu>
 
+    <menu name="YARN Native Services" inherit="top">
+      <item name="Introduction" href="hadoop-yarn/hadoop-yarn-site/native-services/NativeServicesIntro.html"/>
+      <item name="Native Services Discovery" href="hadoop-yarn/hadoop-yarn-site/native-services/NativeServicesDiscovery.html"/>
+    </menu>
+
     <menu name="Hadoop Compatible File Systems" inherit="top">
       <item name="Aliyun OSS" href="hadoop-aliyun/tools/hadoop-aliyun/index.html"/>
       <item name="Amazon S3" href="hadoop-aws/tools/hadoop-aws/index.html"/>

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/markdown/native-services/NativeServicesDiscovery.md

@@ -0,0 +1,127 @@
+# YARN DNS Server
+## Introduction
+
+The YARN DNS Server provides a standard DNS interface to the information posted into the YARN Registry by deployed applications. The DNS service serves the following functions:
+
+1. **Exposing existing service­ discovery information via DNS**​­ - Information provided in
+the current YARN service registry’s records will be converted into DNS entries, thus
+allowing users to discover information about YARN applications using standard DNS
+client mechanisms (for e.g. a DNS SRV Record specifying the hostname and port
+number for services).
+2. **Enabling Container to IP mappings​­** - Enables discovery of the IPs of containers via
+standard DNS lookups. Given the availability of the records via DNS, container
+name­based communication will be facilitated (e.g. ‘curl
+http://myContainer.myDomain.com/endpoint’).
+
+## Service Properties
+
+The existing YARN Service Registry is leveraged as the source of information for the DNS Service.
+
+The following core functions are supported by the DNS­ Server:
+
+###Functional properties
+
+1. Supports creation of DNS records for end­points of the deployed YARN applications
+2. Record names remain unchanged during restart of containers and/or applications
+3. Supports reverse lookups (name based on IP).
+4. Supports security using the standards defined by The Domain Name System Security
+Extensions (DNSSEC)
+5. Highly available
+6. Scalable ­- The service provides the responsiveness (e.g. low­ latency) required to
+respond to DNS queries (timeouts yield attempts to invoke other configured name
+servers).
+
+###Deployment properties
+
+1. Supports integration with existing DNS assets (e.g. a corporate DNS server) by acting as
+a DNS server for a Hadoop cluster zone/domain. The server is not intended to act as a
+primary DNS server and does not forward requests to other servers.
+2. The DNS Server exposes a port that can receive both TCP and UDP requests per
+DNS standards. The default port for DNS protocols is in a restricted, administrative port
+range (53), so the port is configurable for deployments in which the service may
+not be managed via an administrative account.
+
+##DNS Record Name Structure
+
+The DNS names of generated records are composed from the following elements (labels). Note that these elements must be compatible with DNS conventions (see “Preferred Name Syntax” in RFC 1035):
+
+* **domain** -​­ the name of the cluster DNS domain. This name is provided as a
+configuration property. In addition, it is this name that is configured at a parent DNS
+server as the zone name for the defined yDNS zone (the zone for which the parent DNS
+server will forward requests to yDNS). E.g. yarncluster.com
+* **user­name**​ -­ the name of the application deployer. This name is the simple short­name (for
+e.g. the primary component of the Kerberos principal) associated with the user launching
+the application. As the user­name is one of the elements of DNS names, it is expected
+that this also confirms DNS name conventions (RFC 1035 linked above) ­ so special translation is performed for names with special characters like hyphens and spaces.
+* **application ­name** -​­ the name of the deployed YARN application. This name is inferred
+from the YARN registry path to the application's node. Application­ name, rather thn application­ id, was chosen as a way of making it easy for users to refer to human­-readable DNS
+names. This obviously mandates certain uniqueness properties on application­ names.
+* **container id** -​­ the YARN assigned ID to a container (e.g.
+container_e3741_1454001598828_01_000004)
+* **component ­name** -​­ the name assigned to the deployed component (for e.g. a master
+component). A component is a distributed element of an application or service that is
+launched in a YARN container (e.g. an HBase master). One can imagine multiple
+components within an application. A component­ name is not yet a first­ class concept in
+YARN, but is a very useful one that we are introducing here for the sake of yDNS
+entries. Many frameworks like MapReduce, Slider already have component ­names
+(though, as mentioned, they are not yet supported in YARN in a first­ class fashion).
+* **api** -​­ the api designation for the exposed endpoint
+
+###Notes about DNS Names
+
+* In most instances, the DNS names can be easily distinguished by the number of
+elements/labels that compose the name. The cluster’s domain name is always the last
+element. After that element is parsed out, reading from right to left, the first element
+maps to the application ­user and so on. Wherever it is not easily distinguishable, naming conventions are used to disambiguate the name ­using a prefix such as
+“container­” or suffix such as “api”. For example, an endpoint published as a
+management endpoint will be referenced with the name *management­-api.griduser.yarncluster.com​*.
+* Unique application ­name (per user) is not currently supported/guaranteed by YARN, but
+it is supported by frameworks such as Apache Slider. The yDNS service currently
+leverages the last element of the ZK path entry for the application as an
+application­ name. These application­ names have to be unique for a given user.​
+
+##DNS Server Functionality
+
+The primary functions of the DNS service are illustrated in the following diagram:
+
+
+![DNS Functional Overview](../images/dns_overview.png "DNS Functional Overview")
+
+###DNS record creation
+The following figure illustrates at slightly greater detail the DNS record creation and registration sequence (NOTE: service record updates would follow a similar sequence of steps,
+distinguished only by the different event type):
+
+![DNS Functional Overview](../images/dns_record_creation.jpeg "DNS Functional Overview")
+
+###DNS record removal
+Similarly, record removal follows a similar sequence
+
+![DNS Functional Overview](../images/dns_record_removal.jpeg "DNS Functional Overview")
+
+(NOTE: The DNS Zone requires a record as an argument for the deletion method, thus
+requiring similar parsing logic to identify the specific records that should be removed).
+
+###DNS Service initialization
+* The DNS service initializes both UDP and TCP listeners on a configured port. As
+noted above, the default port of 53 is in a restricted range that is only accessible to an
+account with administrative privileges.
+* Subsequently, the DNS service listens for inbound DNS requests. Those requests are
+standard DNS requests from users or other DNS servers (for example, DNS servers that have the
+YARN DNS service configured as a forwarder).
+
+## Configuration
+The YARN DNS server reads its configuration properties from the yarn­site.xml file.  The following are the DNS associated configuration properties:
+
+| Name | Description |
+| ------------ | ------------- |
+| hadoop.registry.dns.enabled | The DNS functionality is enabled for the cluster. Default is false. |
+| hadoop.registry.dns.domain-­name  | The domain name for Hadoop cluster associated records.  |
+| hadoop.registry.dns.bind­-address | Address associated with the network interface to which the DNS listener should bind.  |
+| hadoop.registry.dns.bind-­port | The port number for the DNS listener. The default port is 53. However, since that port falls in a administrator­only range, typical deployments may need to specify an alternate port.  |
+| hadoop.registry.dns.dnssec.enabled | Indicates whether the DNSSEC support is enabled. Default is false.  |
+| hadoop.registry.dns.public­-key  | The base64 representation of the server’s public key. Leveraged for creating the DNSKEY Record provided for DNSSEC client requests.  |
+| hadoop.registry.dns.private-­key-­file  | The path to the standard DNSSEC private key file. Must only be readable by the DNS launching identity. See [dnssec­-keygen](https://ftp.isc.org/isc/bind/cur/9.9/doc/arm/man.dnssec-keygen.html) documentation.  |
+| hadoop.registry.dns­-ttl | The default TTL value to associate with DNS records. The default value is set to 1 (a value of 0 has undefined behavior). A typical value should be approximate to the time it takes YARN to restart a failed container.  |
+| hadoop.registry.dns.zone-­subnet  | An indicator of the IP range associated with the cluster containers. The setting is utilized for the generation of the reverse zone name.  |
+| hadoop.registry.dns.zone-­mask | The network mask associated with the zone IP range.  If specified, it is utilized to ascertain the IP range possible and come up with an appropriate reverse zone name. |
+| hadoop.registry.dns.zones­-dir | A directory containing zone configuration files to read during zone initialization.  This directory can contain zone master files named *zone-name.zone*.  See [here](http://www.zytrax.com/books/dns/ch6/mydomain.html) for zone master file documentation.|