Hadoop in Secure Mode

Introduction

This document describes how to configure authentication for Hadoop in secure mode. When Hadoop is configured to run in secure mode, each Hadoop service and each user must be authenticated by Kerberos.

Forward and reverse host lookup for all service hosts must be configured correctly to allow services to authenticate with each other. Host lookups may be configured using either DNS or /etc/hosts files. Working knowledge of Kerberos and DNS is recommended before attempting to configure Hadoop services in Secure Mode.

Security features of Hadoop consist of Authentication, Service Level Authorization, Authentication for Web Consoles and Data Confidentiality.

Authentication

End User Accounts

When service level authentication is turned on, end users must authenticate themselves before interacting with Hadoop services. The simplest way is for a user to authenticate interactively using the Kerberos kinit command. Programmatic authentication using Kerberos keytab files may be used when interactive login with kinit is infeasible.

User Accounts for Hadoop Daemons

Ensure that HDFS and YARN daemons run as different Unix users, e.g. hdfs and yarn. Also, ensure that the MapReduce JobHistory server runs as different user such as mapred.

It’s recommended to have them share a Unix group, for e.g. hadoop. See also “Mapping from user to group” for group management.

User:Group Daemons
hdfs:hadoop NameNode, Secondary NameNode, JournalNode, DataNode
yarn:hadoop ResourceManager, NodeManager
mapred:hadoop MapReduce JobHistory Server

Kerberos principals for Hadoop Daemons

Each Hadoop Service instance must be configured with its Kerberos principal and keytab file location.

The general format of a Service principal is ServiceName/_HOST@REALM.TLD. e.g. dn/_HOST@EXAMPLE.COM.

Hadoop simplifies the deployment of configuration files by allowing the hostname component of the service principal to be specified as the _HOST wildcard. Each service instance will substitute _HOST with its own fully qualified hostname at runtime. This allows administrators to deploy the same set of configuration files on all nodes. However, the keytab files will be different.

HDFS

The NameNode keytab file, on each NameNode host, should look like the following:

$ klist -e -k -t /etc/security/keytab/nn.service.keytab
Keytab name: FILE:/etc/security/keytab/nn.service.keytab
KVNO Timestamp         Principal
   4 07/18/11 21:08:09 nn/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 nn/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 nn/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)

The Secondary NameNode keytab file, on that host, should look like the following:

$ klist -e -k -t /etc/security/keytab/sn.service.keytab
Keytab name: FILE:/etc/security/keytab/sn.service.keytab
KVNO Timestamp         Principal
   4 07/18/11 21:08:09 sn/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 sn/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 sn/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)

The DataNode keytab file, on each host, should look like the following:

$ klist -e -k -t /etc/security/keytab/dn.service.keytab
Keytab name: FILE:/etc/security/keytab/dn.service.keytab
KVNO Timestamp         Principal
   4 07/18/11 21:08:09 dn/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 dn/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 dn/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)

YARN

The ResourceManager keytab file, on the ResourceManager host, should look like the following:

$ klist -e -k -t /etc/security/keytab/rm.service.keytab
Keytab name: FILE:/etc/security/keytab/rm.service.keytab
KVNO Timestamp         Principal
   4 07/18/11 21:08:09 rm/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 rm/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 rm/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)

The NodeManager keytab file, on each host, should look like the following:

$ klist -e -k -t /etc/security/keytab/nm.service.keytab
Keytab name: FILE:/etc/security/keytab/nm.service.keytab
KVNO Timestamp         Principal
   4 07/18/11 21:08:09 nm/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 nm/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 nm/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)

MapReduce JobHistory Server

The MapReduce JobHistory Server keytab file, on that host, should look like the following:

$ klist -e -k -t /etc/security/keytab/jhs.service.keytab
Keytab name: FILE:/etc/security/keytab/jhs.service.keytab
KVNO Timestamp         Principal
   4 07/18/11 21:08:09 jhs/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 jhs/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 jhs/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-256 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (AES-128 CTS mode with 96-bit SHA-1 HMAC)
   4 07/18/11 21:08:09 host/full.qualified.domain.name@REALM.TLD (ArcFour with HMAC/md5)

Mapping from Kerberos principals to OS user accounts

Hadoop maps Kerberos principals to OS user (system) accounts using rules specified by hadoop.security.auth_to_local. These rules work in the same way as the auth_to_local in Kerberos configuration file (krb5.conf). In addition, Hadoop auth_to_local mapping supports the /L flag that lowercases the returned name.

The default is to pick the first component of the principal name as the system user name if the realm matches the default_realm (usually defined in /etc/krb5.conf). e.g. The default rule maps the principal host/full.qualified.domain.name@REALM.TLD to system user host. The default rule will not be appropriate for most clusters.

In a typical cluster HDFS and YARN services will be launched as the system hdfs and yarn users respectively. hadoop.security.auth_to_local can be configured as follows:

<property>
  <name>hadoop.security.auth_to_local</name>
  <value>
    RULE:[2:$1@$0](nn/.*@.*REALM.TLD)s/.*/hdfs/
    RULE:[2:$1@$0](jn/.*@.*REALM.TLD)s/.*/hdfs/
    RULE:[2:$1@$0](dn/.*@.*REALM.TLD)s/.*/hdfs/
    RULE:[2:$1@$0](nm/.*@.*REALM.TLD)s/.*/yarn/
    RULE:[2:$1@$0](rm/.*@.*REALM.TLD)s/.*/yarn/
    RULE:[2:$1@$0](jhs/.*@.*REALM.TLD)s/.*/mapred/
    DEFAULT
  </value>
</property>

Custom rules can be tested using the hadoop kerbname command. This command allows one to specify a principal and apply Hadoop’s current auth_to_local ruleset.

Mapping from user to group

The system user to system group mapping mechanism can be configured via hadoop.security.group.mapping. See Hadoop Groups Mapping for details.

Practically you need to manage SSO environment using Kerberos with LDAP for Hadoop in secure mode.

Proxy user

Some products such as Apache Oozie which access the services of Hadoop on behalf of end users need to be able to impersonate end users. See the doc of proxy user for details.

Secure DataNode

Because the DataNode data transfer protocol does not use the Hadoop RPC framework, DataNodes must authenticate themselves using privileged ports which are specified by dfs.datanode.address and dfs.datanode.http.address. This authentication is based on the assumption that the attacker won’t be able to get root privileges on DataNode hosts.

When you execute the hdfs datanode command as root, the server process binds privileged ports at first, then drops privilege and runs as the user account specified by HDFS_DATANODE_SECURE_USER. This startup process uses the jsvc program installed to JSVC_HOME. You must specify HDFS_DATANODE_SECURE_USER and JSVC_HOME as environment variables on start up (in hadoop-env.sh).

As of version 2.6.0, SASL can be used to authenticate the data transfer protocol. In this configuration, it is no longer required for secured clusters to start the DataNode as root using jsvc and bind to privileged ports. To enable SASL on data transfer protocol, set dfs.data.transfer.protection in hdfs-site.xml, set a non-privileged port for dfs.datanode.address, set dfs.http.policy to HTTPS_ONLY and make sure the HDFS_DATANODE_SECURE_USER environment variable is not defined. Note that it is not possible to use SASL on data transfer protocol if dfs.datanode.address is set to a privileged port. This is required for backwards-compatibility reasons.

In order to migrate an existing cluster that used root authentication to start using SASL instead, first ensure that version 2.6.0 or later has been deployed to all cluster nodes as well as any external applications that need to connect to the cluster. Only versions 2.6.0 and later of the HDFS client can connect to a DataNode that uses SASL for authentication of data transfer protocol, so it is vital that all callers have the correct version before migrating. After version 2.6.0 or later has been deployed everywhere, update configuration of any external applications to enable SASL. If an HDFS client is enabled for SASL, then it can connect successfully to a DataNode running with either root authentication or SASL authentication. Changing configuration for all clients guarantees that subsequent configuration changes on DataNodes will not disrupt the applications. Finally, each individual DataNode can be migrated by changing its configuration and restarting. It is acceptable to have a mix of some DataNodes running with root authentication and some DataNodes running with SASL authentication temporarily during this migration period, because an HDFS client enabled for SASL can connect to both.

Data confidentiality

Data Encryption on RPC

The data transfered between hadoop services and clients can be encrypted on the wire. Setting hadoop.rpc.protection to privacy in core-site.xml activates data encryption.

Data Encryption on Block data transfer.

You need to set dfs.encrypt.data.transfer to true in the hdfs-site.xml in order to activate data encryption for data transfer protocol of DataNode.

Optionally, you may set dfs.encrypt.data.transfer.algorithm to either 3des or rc4 to choose the specific encryption algorithm. If unspecified, then the configured JCE default on the system is used, which is usually 3DES.

Setting dfs.encrypt.data.transfer.cipher.suites to AES/CTR/NoPadding activates AES encryption. By default, this is unspecified, so AES is not used. When AES is used, the algorithm specified in dfs.encrypt.data.transfer.algorithm is still used during an initial key exchange. The AES key bit length can be configured by setting dfs.encrypt.data.transfer.cipher.key.bitlength to 128, 192 or 256. The default is 128.

AES offers the greatest cryptographic strength and the best performance. At this time, 3DES and RC4 have been used more often in Hadoop clusters.

Data Encryption on HTTP

Data transfer between Web-console and clients are protected by using SSL(HTTPS). SSL configuration is recommended but not required to configure Hadoop security with Kerberos.

To enable SSL for web console of HDFS daemons, set dfs.http.policy to either HTTPS_ONLY or HTTP_AND_HTTPS in hdfs-site.xml. Note KMS and HttpFS do not respect this parameter. See Hadoop KMS and Hadoop HDFS over HTTP - Server Setup for instructions on enabling KMS over HTTPS and HttpFS over HTTPS, respectively.

To enable SSL for web console of YARN daemons, set yarn.http.policy to HTTPS_ONLY in yarn-site.xml.

To enable SSL for web console of MapReduce JobHistory server, set mapreduce.jobhistory.http.policy to HTTPS_ONLY in mapred-site.xml.

Configuration

Permissions for both HDFS and local fileSystem paths

The following table lists various paths on HDFS and local filesystems (on all nodes) and recommended permissions:

Filesystem Path User:Group Permissions
local dfs.namenode.name.dir hdfs:hadoop drwx------
local dfs.datanode.data.dir hdfs:hadoop drwx------
local $HADOOP_LOG_DIR hdfs:hadoop drwxrwxr-x
local $YARN_LOG_DIR yarn:hadoop drwxrwxr-x
local yarn.nodemanager.local-dirs yarn:hadoop drwxr-xr-x
local yarn.nodemanager.log-dirs yarn:hadoop drwxr-xr-x
local container-executor root:hadoop --Sr-s--*
local conf/container-executor.cfg root:hadoop r-------*
hdfs / hdfs:hadoop drwxr-xr-x
hdfs /tmp hdfs:hadoop drwxrwxrwxt
hdfs /user hdfs:hadoop drwxr-xr-x
hdfs yarn.nodemanager.remote-app-log-dir yarn:hadoop drwxrwxrwxt
hdfs mapreduce.jobhistory.intermediate-done-dir mapred:hadoop drwxrwxrwxt
hdfs mapreduce.jobhistory.done-dir mapred:hadoop drwxr-x---

Common Configurations

In order to turn on RPC authentication in hadoop, set the value of hadoop.security.authentication property to "kerberos", and set security related settings listed below appropriately.

The following properties should be in the core-site.xml of all the nodes in the cluster.

Parameter Value Notes
hadoop.security.authentication kerberos simple : No authentication. (default)  kerberos : Enable authentication by Kerberos.
hadoop.security.authorization true Enable RPC service-level authorization.
hadoop.rpc.protection authentication authentication : authentication only (default); integrity : integrity check in addition to authentication; privacy : data encryption in addition to integrity
hadoop.security.auth_to_local RULE:exp1 RULE:exp2  DEFAULT The value is string containing new line characters. See Kerberos documentation for the format of exp.
hadoop.proxyuser.superuser.hosts comma separated hosts from which superuser access are allowed to impersonation. * means wildcard.
hadoop.proxyuser.superuser.groups comma separated groups to which users impersonated by superuser belong. * means wildcard.

NameNode

Parameter Value Notes
dfs.block.access.token.enable true Enable HDFS block access tokens for secure operations.
dfs.namenode.kerberos.principal nn/_HOST@REALM.TLD Kerberos principal name for the NameNode.
dfs.namenode.keytab.file /etc/security/keytab/nn.service.keytab Kerberos keytab file for the NameNode.
dfs.namenode.kerberos.internal.spnego.principal HTTP/_HOST@REALM.TLD The server principal used by the NameNode for web UI SPNEGO authentication. The SPNEGO server principal begins with the prefix HTTP/ by convention. If the value is '*', the web server will attempt to login with every principal specified in the keytab file dfs.web.authentication.kerberos.keytab. For most deployments this can be set to ${dfs.web.authentication.kerberos.principal} i.e use the value of dfs.web.authentication.kerberos.principal.
dfs.web.authentication.kerberos.keytab /etc/security/keytab/spnego.service.keytab SPNEGO keytab file for the NameNode. In HA clusters this setting is shared with the Journal Nodes.

The following settings allow configuring SSL access to the NameNode web UI (optional).

Parameter Value Notes
dfs.http.policy HTTP_ONLY or HTTPS_ONLY or HTTP_AND_HTTPS HTTPS_ONLY turns off http access. This option takes precedence over the deprecated configuration dfs.https.enable and hadoop.ssl.enabled. If using SASL to authenticate data transfer protocol instead of running DataNode as root and using privileged ports, then this property must be set to HTTPS_ONLY to guarantee authentication of HTTP servers. (See dfs.data.transfer.protection.)
dfs.namenode.https-address 0.0.0.0:9871 This parameter is used in non-HA mode and without federation. See HDFS High Availability and HDFS Federation for details.
dfs.https.enable true This value is deprecated. Use dfs.http.policy

Secondary NameNode

Parameter Value Notes
dfs.namenode.secondary.http-address 0.0.0.0:9868 HTTP web UI address for the Secondary NameNode.
dfs.namenode.secondary.https-address 0.0.0.0:9869 HTTPS web UI address for the Secondary NameNode.
dfs.secondary.namenode.keytab.file /etc/security/keytab/sn.service.keytab Kerberos keytab file for the Secondary NameNode.
dfs.secondary.namenode.kerberos.principal sn/_HOST@REALM.TLD Kerberos principal name for the Secondary NameNode.
dfs.secondary.namenode.kerberos.internal.spnego.principal HTTP/_HOST@REALM.TLD The server principal used by the Secondary NameNode for web UI SPNEGO authentication. The SPNEGO server principal begins with the prefix HTTP/ by convention. If the value is '*', the web server will attempt to login with every principal specified in the keytab file dfs.web.authentication.kerberos.keytab. For most deployments this can be set to ${dfs.web.authentication.kerberos.principal} i.e use the value of dfs.web.authentication.kerberos.principal.

JournalNode

Parameter Value Notes
dfs.journalnode.kerberos.principal jn/_HOST@REALM.TLD Kerberos principal name for the JournalNode.
dfs.journalnode.keytab.file /etc/security/keytab/jn.service.keytab Kerberos keytab file for the JournalNode.
dfs.journalnode.kerberos.internal.spnego.principal HTTP/_HOST@REALM.TLD The server principal used by the JournalNode for web UI SPNEGO authentication when Kerberos security is enabled. The SPNEGO server principal begins with the prefix HTTP/ by convention. If the value is '*', the web server will attempt to login with every principal specified in the keytab file dfs.web.authentication.kerberos.keytab. For most deployments this can be set to ${dfs.web.authentication.kerberos.principal} i.e use the value of dfs.web.authentication.kerberos.principal.
dfs.web.authentication.kerberos.keytab /etc/security/keytab/spnego.service.keytab SPNEGO keytab file for the JournalNode. In HA clusters this setting is shared with the Name Nodes.
dfs.journalnode.https-address 0.0.0.0:8481 HTTPS web UI address for the JournalNode.

DataNode

Parameter Value Notes
dfs.datanode.data.dir.perm 700
dfs.datanode.address 0.0.0.0:1004 Secure DataNode must use privileged port in order to assure that the server was started securely. This means that the server must be started via jsvc. Alternatively, this must be set to a non-privileged port if using SASL to authenticate data transfer protocol. (See dfs.data.transfer.protection.)
dfs.datanode.http.address 0.0.0.0:1006 Secure DataNode must use privileged port in order to assure that the server was started securely. This means that the server must be started via jsvc.
dfs.datanode.https.address 0.0.0.0:9865 HTTPS web UI address for the Data Node.
dfs.datanode.kerberos.principal dn/_HOST@REALM.TLD Kerberos principal name for the DataNode.
dfs.datanode.keytab.file /etc/security/keytab/dn.service.keytab Kerberos keytab file for the DataNode.
dfs.encrypt.data.transfer false set to true when using data encryption
dfs.encrypt.data.transfer.algorithm optionally set to 3des or rc4 when using data encryption to control encryption algorithm
dfs.encrypt.data.transfer.cipher.suites optionally set to AES/CTR/NoPadding to activate AES encryption when using data encryption
dfs.encrypt.data.transfer.cipher.key.bitlength optionally set to 128, 192 or 256 to control key bit length when using AES with data encryption
dfs.data.transfer.protection authentication : authentication only; integrity : integrity check in addition to authentication; privacy : data encryption in addition to integrity This property is unspecified by default. Setting this property enables SASL for authentication of data transfer protocol. If this is enabled, then dfs.datanode.address must use a non-privileged port, dfs.http.policy must be set to HTTPS_ONLY and the HDFS_DATANODE_SECURE_USER environment variable must be undefined when starting the DataNode process.

WebHDFS

Parameter Value Notes
dfs.web.authentication.kerberos.principal http/_HOST@REALM.TLD Kerberos principal name for the WebHDFS. In HA clusters this setting is commonly used by the JournalNodes for securing access to the JournalNode HTTP server with SPNEGO.
dfs.web.authentication.kerberos.keytab /etc/security/keytab/http.service.keytab Kerberos keytab file for WebHDFS. In HA clusters this setting is commonly used the JournalNodes for securing access to the JournalNode HTTP server with SPNEGO.

ResourceManager

Parameter Value Notes
yarn.resourcemanager.principal rm/_HOST@REALM.TLD Kerberos principal name for the ResourceManager.
yarn.resourcemanager.keytab /etc/security/keytab/rm.service.keytab Kerberos keytab file for the ResourceManager.
yarn.resourcemanager.webapp.https.address ${yarn.resourcemanager.hostname}:8090 The https adddress of the RM web application for non-HA. In HA clusters, use yarn.resourcemanager.webapp.https.address.rm-id for each ResourceManager. See ResourceManager High Availability for details.

NodeManager

Parameter Value Notes
yarn.nodemanager.principal nm/_HOST@REALM.TLD Kerberos principal name for the NodeManager.
yarn.nodemanager.keytab /etc/security/keytab/nm.service.keytab Kerberos keytab file for the NodeManager.
yarn.nodemanager.container-executor.class org.apache.hadoop.yarn.server.nodemanager.LinuxContainerExecutor Use LinuxContainerExecutor.
yarn.nodemanager.linux-container-executor.group hadoop Unix group of the NodeManager.
yarn.nodemanager.linux-container-executor.path /path/to/bin/container-executor The path to the executable of Linux container executor.
yarn.nodemanager.webapp.https.address 0.0.0.0:8044 The https adddress of the NM web application.

Configuration for WebAppProxy

The WebAppProxy provides a proxy between the web applications exported by an application and an end user. If security is enabled it will warn users before accessing a potentially unsafe web application. Authentication and authorization using the proxy is handled just like any other privileged web application.

Parameter Value Notes
yarn.web-proxy.address WebAppProxy host:port for proxy to AM web apps. host:port if this is the same as yarn.resourcemanager.webapp.address or it is not defined then the ResourceManager will run the proxy otherwise a standalone proxy server will need to be launched.
yarn.web-proxy.keytab /etc/security/keytab/web-app.service.keytab Kerberos keytab file for the WebAppProxy.
yarn.web-proxy.principal wap/_HOST@REALM.TLD Kerberos principal name for the WebAppProxy.

LinuxContainerExecutor

A ContainerExecutor used by YARN framework which define how any container launched and controlled.

The following are the available in Hadoop YARN:

ContainerExecutor Description
DefaultContainerExecutor The default executor which YARN uses to manage container execution. The container process has the same Unix user as the NodeManager.
LinuxContainerExecutor Supported only on GNU/Linux, this executor runs the containers as either the YARN user who submitted the application (when full security is enabled) or as a dedicated user (defaults to nobody) when full security is not enabled. When full security is enabled, this executor requires all user accounts to be created on the cluster nodes where the containers are launched. It uses a setuid executable that is included in the Hadoop distribution. The NodeManager uses this executable to launch and kill containers. The setuid executable switches to the user who has submitted the application and launches or kills the containers. For maximum security, this executor sets up restricted permissions and user/group ownership of local files and directories used by the containers such as the shared objects, jars, intermediate files, log files etc. Particularly note that, because of this, except the application owner and NodeManager, no other user can access any of the local files/directories including those localized as part of the distributed cache.

To build the LinuxContainerExecutor executable run:

 $ mvn package -Dcontainer-executor.conf.dir=/etc/hadoop/

The path passed in -Dcontainer-executor.conf.dir should be the path on the cluster nodes where a configuration file for the setuid executable should be located. The executable should be installed in $HADOOP_YARN_HOME/bin.

The executable must have specific permissions: 6050 or --Sr-s--- permissions user-owned by root (super-user) and group-owned by a special group (e.g. hadoop) of which the NodeManager Unix user is the group member and no ordinary application user is. If any application user belongs to this special group, security will be compromised. This special group name should be specified for the configuration property yarn.nodemanager.linux-container-executor.group in both conf/yarn-site.xml and conf/container-executor.cfg.

For example, let’s say that the NodeManager is run as user yarn who is part of the groups users and hadoop, any of them being the primary group. Let also be that users has both yarn and another user (application submitter) alice as its members, and alice does not belong to hadoop. Going by the above description, the setuid/setgid executable should be set 6050 or --Sr-s--- with user-owner as yarn and group-owner as hadoop which has yarn as its member (and not users which has alice also as its member besides yarn).

The LinuxTaskController requires that paths including and leading up to the directories specified in yarn.nodemanager.local-dirs and yarn.nodemanager.log-dirs to be set 755 permissions as described above in the table on permissions on directories.

  • conf/container-executor.cfg

The executable requires a configuration file called container-executor.cfg to be present in the configuration directory passed to the mvn target mentioned above.

The configuration file must be owned by the user running NodeManager (user yarn in the above example), group-owned by anyone and should have the permissions 0400 or r-------- .

The executable requires following configuration items to be present in the conf/container-executor.cfg file. The items should be mentioned as simple key=value pairs, one per-line:

Parameter Value Notes
yarn.nodemanager.linux-container-executor.group hadoop Unix group of the NodeManager. The group owner of the container-executor binary should be this group. Should be same as the value with which the NodeManager is configured. This configuration is required for validating the secure access of the container-executor binary.
banned.users hdfs,yarn,mapred,bin Banned users.
allowed.system.users foo,bar Allowed system users.
min.user.id 1000 Prevent other super-users.

To re-cap, here are the local file-sysytem permissions required for the various paths related to the LinuxContainerExecutor:

Filesystem Path User:Group Permissions
local container-executor root:hadoop --Sr-s--*
local conf/container-executor.cfg root:hadoop r-------*
local yarn.nodemanager.local-dirs yarn:hadoop drwxr-xr-x
local yarn.nodemanager.log-dirs yarn:hadoop drwxr-xr-x

MapReduce JobHistory Server

Parameter Value Notes
mapreduce.jobhistory.address MapReduce JobHistory Server host:port Default port is 10020.
mapreduce.jobhistory.keytab /etc/security/keytab/jhs.service.keytab Kerberos keytab file for the MapReduce JobHistory Server.
mapreduce.jobhistory.principal jhs/_HOST@REALM.TLD Kerberos principal name for the MapReduce JobHistory Server.

Multihoming

Multihomed setups where each host has multiple hostnames in DNS (e.g. different hostnames corresponding to public and private network interfaces) may require additional configuration to get Kerberos authentication working. See HDFS Support for Multihomed Networks

Troubleshooting

Kerberos is hard to set up —and harder to debug. Common problems are

  1. Network and DNS configuration.
  2. Kerberos configuration on hosts (/etc/krb5.conf).
  3. Keytab creation and maintenance.
  4. Environment setup: JVM, user login, system clocks, etc.

The fact that the error messages from the JVM are essentially meaningless does not aid in diagnosing and fixing such problems.

Extra debugging information can be enabled for the client and for any service

Set the environment variable HADOOP_JAAS_DEBUG to true.

export HADOOP_JAAS_DEBUG=true

Edit the log4j.properties file to log Hadoop’s security package at DEBUG level.

log4j.logger.org.apache.hadoop.security=DEBUG

Enable JVM-level debugging by setting some system properties.

export HADOOP_OPTS="-Djava.net.preferIPv4Stack=true -Dsun.security.krb5.debug=true -Dsun.security.spnego.debug"

Troubleshooting with KDiag

Hadoop has a tool to aid validating setup: KDiag

It contains a series of probes for the JVM’s configuration and the environment, dumps out some system files (/etc/krb5.conf, /etc/ntp.conf), prints out some system state and then attempts to log in to Kerberos as the current user, or a specific principal in a named keytab.

The output of the command can be used for local diagnostics, or forwarded to whoever supports the cluster.

The KDiag command has its own entry point; it is currently not hooked up to the end-user CLI.

It is invoked simply by passing its full classname to one of the bin/hadoop, bin/hdfs or bin/yarn commands. Accordingly, it will display the kerberos client state of the command used to invoke it.

hadoop org.apache.hadoop.security.KDiag
hdfs org.apache.hadoop.security.KDiag
yarn org.apache.hadoop.security.KDiag

The command returns a status code of 0 for a successful diagnostics run. This does not imply that Kerberos is working —merely that the KDiag command did not identify any problem from its limited set of probes. In particular, as it does not attempt to connect to any remote service, it does not verify that the client is trusted by any service.

If unsuccessful, exit codes are

  • -1: the command failed for an unknown reason
  • 41: Unauthorized (== HTTP’s 401). KDiag detected a condition which causes Kerberos to not work. Examine the output to identify the issue.

Usage

KDiag: Diagnose Kerberos Problems
  [-D key=value] : Define a configuration option.
  [--jaas] : Require a JAAS file to be defined in java.security.auth.login.config.
  [--keylen <keylen>] : Require a minimum size for encryption keys supported by the JVM. Default value : 256.
  [--keytab <keytab> --principal <principal>] : Login from a keytab as a specific principal.
  [--nofail] : Do not fail on the first problem.
  [--nologin] : Do not attempt to log in.
  [--out <file>] : Write output to a file.
  [--resource <resource>] : Load an XML configuration resource.
  [--secure] : Require the hadoop configuration to be secure.
  [--verifyshortname <principal>]: Verify the short name of the specific principal does not contain '@' or '/'

--jaas: Require a JAAS file to be defined in java.security.auth.login.config.

If --jaas is set, the Java system property java.security.auth.login.config must be set to a JAAS file; this file must exist, be a simple file of non-zero bytes, and readable by the current user. More detailed validation is not performed.

JAAS files are not needed by Hadoop itself, but some services (such as Zookeeper) do require them for secure operation.

--keylen <length>: Require a minimum size for encryption keys supported by the JVM".

If the JVM does not support this length, the command will fail.

The default value is to 256, as needed for the AES256 encryption scheme. A JVM without the Java Cryptography Extensions installed does not support such a key length. Kerberos will not work unless configured to use an encryption scheme with a shorter key length.

--keytab <keytab> --principal <principal>: Log in from a keytab.

Log in from a keytab as the specific principal.

  1. The file must contain the specific principal, including any named host. That is, there is no mapping from _HOST to the current hostname.
  2. KDiag will log out and attempt to log back in again. This catches JVM compatibility problems which have existed in the past. (Hadoop’s Kerberos support requires use of/introspection into JVM-specific classes).

--nofail : Do not fail on the first problem

KDiag will make a best-effort attempt to diagnose all Kerberos problems, rather than stop at the first one.

This is somewhat limited; checks are made in the order which problems surface (e.g keylength is checked first), so an early failure can trigger many more problems. But it does produce a more detailed report.

--nologin: Do not attempt to log in.

Skip trying to log in. This takes precedence over the --keytab option, and also disables trying to log in to kerberos as the current kinited user.

This is useful when the KDiag command is being invoked within an application, as it does not set up Hadoop’s static security state —merely check for some basic Kerberos preconditions.

--out outfile: Write output to file.

hadoop org.apache.hadoop.security.KDiag --out out.txt

Much of the diagnostics information comes from the JRE (to stderr) and from Log4j (to stdout). To get all the output, it is best to redirect both these output streams to the same file, and omit the --out option.

hadoop org.apache.hadoop.security.KDiag --keytab zk.service.keytab --principal zookeeper/devix.example.org@REALM > out.txt 2>&1

Even there, the output of the two streams, emitted across multiple threads, can be a bit confusing. It will get easier with practise. Looking at the thread name in the Log4j output to distinguish background threads from the main thread helps at the hadoop level, but doesn’t assist in JVM-level logging.

--resource <resource> : XML configuration resource to load.

When using the hdfs and yarn commands, it is often useful to force load the hdfs-site.xml and yarn-site.xml resource files, to pick up any Kerberos-related configuration options therein. The core-default and core-site XML resources are always loaded.

hdfs org.apache.hadoop.security.KDiag --resource hbase-default.xml --resource hbase-site.xml
yarn org.apache.hadoop.security.KDiag --resource yarn-default.xml --resource yarn-site.xml

For extra logging during the operation, set the logging and HADOOP_JAAS_DEBUG environment variable to the values listed in “Troubleshooting”. The JVM options are automatically set in KDiag.

--secure: Fail if the command is not executed on a secure cluster.

That is: if the authentication mechanism of the cluster is explicitly or implicitly set to “simple”:

<property>
  <name>hadoop.security.authentication</name>
  <value>simple</value>
</property>

Needless to say, an application so configured cannot talk to a secure Hadoop cluster.

--verifyshortname &lt;principal>: validate the short name of a principal

This verifies that the short name of a principal contains neither the "@" nor "/" characters.

Example

hdfs org.apache.hadoop.security.KDiag \
  --nofail \
  --resource hbase-default.xml --resource hbase-site.xml \
  --keylen 1024 \
  --keytab zk.service.keytab --principal zookeeper/devix.example.org@REALM

This attempts to to perform all diagnostics without failing early, load in the HDFS and YARN XML resources, require a minimum key length of 1024 bytes, and log in as the principal zookeeper/devix.example.org@REALM, whose key must be in the keytab zk.service.keytab