两个Hadoop集群开启Kerberos验证后，集群间不能够相互访问，需要实现Kerberos之间的互信，使用Hadoop集群A的客户端访问Hadoop集群B的服务（实质上是使用Kerberos Realm A上的Ticket实现访问Realm B的服务）。
先决条件：
1）两个集群(IDC.COM和HADOOP.COM)均开启Kerberos认证
2）Kerberos的REALM分别设置为IDC.COM和HADOOP.COM
步骤如下：
1 配置KDC之间的信任ticket
实现DIDC.COM和HADOOP.COM之间的跨域互信，例如使用IDC.COM的客户端访问HADOOP.COM中的服务，两个REALM需要共同拥有名为krbtgt/HADOOP.COM@IDC.COM的principal，两个Keys需要保证密码，version number和加密方式一致。默认情况下互信是单向的， HADOOP.COM的客户端访问IDC.COM的服务，两个REALM需要有krbtgt/IDC.COM@HADOOP.COM的principal。
向两个集群中添加krbtgt principal
#IDC CLUSTER
kadmin.local: addprinc –e “aes128-cts:normal des3-hmac-sha1:normal arcfour-hmac:normal camellia256-cts:normal camellia128-cts:normal des-hmac-sha1:normal des-cbc-md5:normal ” krbtgt/HADOOP.COM@IDC.COM
kadmin.local: addprinc –e “aes128-cts:normal des3-hmac-sha1:normal arcfour-hmac:normal camellia256-cts:normal camellia128-cts:normal des-hmac-sha1:normal des-cbc-md5:normal ” krbtgt/IDC.COM@HADOOP.COM
#HADOOP CLUSTER
kadmin.local: addprinc –e “aes128-cts:normal des3-hmac-sha1:normal arcfour-hmac:normal camellia256-cts:normal camellia128-cts:normal des-hmac-sha1:normal des-cbc-md5:normal ” krbtgt/HADOOP.COM@IDC.COM
kadmin.local: addprinc –e “aes128-cts:normal des3-hmac-sha1:normal arcfour-hmac:normal camellia256-cts:normal camellia128-cts:normal des-hmac-sha1:normal des-cbc-md5:normal ” krbtgt/IDC.COM@HADOOP.COM
要验证两个entries具有匹配的kvno和加密type，查看命令使用getprinc <principal_name>
kadmin.local: getprinc krbtgt/IDC.COM@HADOOP.COM
Principal: krbtgt/IDC.COM@HADOOP.COM
Expiration date: [never]
Last password change: Wed Jul 05 14:18:11 CST 2017
Password expiration date: [none]
Maximum ticket life: 1 day 00:00:00
Maximum renewable life: 30 days 00:00:00
Last modified: Wed Jul 05 14:18:11 CST 2017 (admin/admin@IDC.COM)
Last successful authentication: [never]
Last failed authentication: [never]
Failed password attempts: 0
Number of keys: 7
Key: vno 1, aes128-cts-hmac-sha1-96
Key: vno 1, des3-cbc-sha1
Key: vno 1, arcfour-hmac
Key: vno 1, camellia256-cts-cmac
Key: vno 1, camellia128-cts-cmac
Key: vno 1, des-hmac-sha1
Key: vno 1, des-cbc-md5
MKey: vno 1
Attributes:
Policy: [none]
kadmin.local: getprinc addprinc krbtgt/HADOOP.COM@IDC.COM
usage: get_principal [-terse] principal
kadmin.local: getprinc krbtgt/HADOOP.COM@IDC.COM
Principal: krbtgt/HADOOP.COM@IDC.COM
Expiration date: [never]
Last password change: Wed Jul 05 14:17:47 CST 2017
Password expiration date: [none]
Maximum ticket life: 1 day 00:00:00
Maximum renewable life: 30 days 00:00:00
Last modified: Wed Jul 05 14:17:47 CST 2017 (admin/admin@IDC.COM)
Last successful authentication: [never]
Last failed authentication: [never]
Failed password attempts: 0
Number of keys: 7
Key: vno 1, aes128-cts-hmac-sha1-96
Key: vno 1, des3-cbc-sha1
Key: vno 1, arcfour-hmac
Key: vno 1, camellia256-cts-cmac
Key: vno 1, camellia128-cts-cmac
Key: vno 1, des-hmac-sha1
Key: vno 1, des-cbc-md5
MKey: vno 1
Attributes:
Policy: [none]
2 在core-site中配置principal和user的映射RULES
设置hadoop.security.auth_to_local参数，该参数用于将principal转变为user，一个需要注意的问题是SASL RPC客户端需要远程Server的Kerberos principal在本身的配置中匹配该principal。相同的pricipal name需要分配给源和目标cluster的服务，例如Source Cluster中的NameNode的kerbeors principal name为nn/h@IDC.COM，在Destination cluster中NameNode的pricipal设置为nn/h@HADOOP.COM（不能设置为nn2/h***@HADOOP.COM），例如：
在IDC Cluster和 HADOOP Cluster的core-site中增加：
<property>
<name>hadoop.security.auth_to_local</name>
<value>
RULE:[1:$1@$0](^.*@HADOOP\.COM$)s/^(.*)@HADOOP\.COM$/$1/g
RULE:[2:$1@$0](^.*@HADOOP\.COM$)s/^(.*)@HADOOP\.COM$/$1/g
RULE:[1:$1@$0](^.*@IDC\.COM$)s/^(.*)@IDC\.COM$/$1/g
RULE:[2:$1@$0](^.*@IDC\.COM$)s/^(.*)@IDC\.COM$/$1/g
DEFAULT
</value>
</property>
使用hadoop org.apache.hadoop.security.HadoopKerberosName 来实现验证，例如:
[root@node1a141 ~]# hadoop org.apache.hadoop.security.HadoopKerberosName hdfs/nodea1a141@IDC.COM
Name: hdfs/nodea1a141@IDC.COM to hdfs
3 在krb5.conf中配置信任关系
3.1 配置capaths
第一种方式是配置shared hierarchy of names，这个是默认及比较简单的方式，第二种方式是在krb5.conf文件中改变capaths，复杂但是比较灵活，这里采用第二种方式。
在两个集群的节点的/etc/krb5.conf文件配置domain和realm的映射关系，例如：在IDC cluster中配置：
[capaths]
IDC.COM = {
HADOOP.COM = .
}
在HADOOP Cluster中配置：
[capaths]
HADOOP.COM = {
IDC.COM = .
}
配置成'.'是表示没有intermediate realms
3.2 配置realms
为了是IDC 可以访问HADOOP的KDC，需要将HADOOP的KDC Server配置到IDC cluster中，如下，反之相同：
[realms]
IDC.COM = {
kdc = {host}.IDC.COM:88
admin_server = {host}.IDC.COM:749
default_domain = IDC.COM
}
HADOOP.COM = {
kdc = {host}.HADOOP.COM:88
admin_server = {host}.HADOOP.COM:749
default_domain = HADOOP.COM
}
3.3 配置domain_realm
在domain_realm中，一般配置成'.IDC.COM'和'IDC.COM'的格式，'.'前缀保证kerberos将所有的IDC.COM的主机均映射到IDC.COM realm。但是如果集群中的主机名不是以IDC.COM为后缀的格式，那么需要在domain_realm中配置主机与realm的映射关系，例IDC.nn.local映射为IDC.COM，需要增加IDC.nn.local = IDC.COM。
[domain_realm]
.hadoop.com=HADOOP.COM
hadoop.com=HADOOP.COM
.IDC.com=IDC.COM
IDC.com=IDC.COM
node1a141 = IDC.COM
node1a143 = IDC.COM
node1a210 = HADOOP.COM
node1a202 = HADOOP.COM
node1a203 = HADOOP.COM
重启kerberos服务
3.4 配置hdfs-site.xml
在hdfs-site.xml，设置允许的realms
在hdfs-site.xml中设置dfs.namenode.kerberos.principal.pattern为"*"
这个是客户端的匹配规则用于控制允许的认证realms，如果该参数不配置，会有下面的异常：
java.io.IOException: Failed on local exception: java.io.IOException:
java.lang.IllegalArgumentException:
Server has invalid Kerberosprincipal:nn/ HADOOP.COM@ IDC.COM;
Host Details : local host is: "host1.IDC.COM/10.181.22.130";
destination host is: "host2.HADOOP.COM":8020;
4 测试
1)使用hdfs命令测试IDC 和HADOOP 集群间的数据访问
例如在IDC Cluster中kinit admin@IDC.COM，然后运行hdfs命令，查看本机群和对方集群得hdfs目录：
如果未开启跨域互信，访问对方hdfs目录时会报认证错误
[root@node1a141 ~]# kdestroy
在本机群客户端登陆admin用户,通过kerberos认证
[root@node1a141 ~]# kinit admin
Password for admin@IDC.COM:
访问本集群hdfs
[root@node1a141 ~]# hdfs dfs -ls /
Found 3 items
drwxrwxrwx+ - hdfs supergroup 0 2017-06-13 15:13 /tmp
drwxrwxr-x+ - hdfs supergroup 0 2017-06-22 15:55 /user
drwxrwxr-x+ - hdfs supergroup 0 2017-06-14 14:11 /wa
访问对方集群hdfs
[root@node1a141 ~]# hdfs dfs -ls hdfs://node1a202:8020/
Found 9 items
drwxr-xr-x - root supergroup 0 2017-05-27 18:55 hdfs://node1a202:8020/cdtest
drwx------ - hbase hbase 0 2017-05-22 18:51 hdfs://node1a202:8020/hbase
drwx------ - hbase hbase 0 2017-07-05 19:16 hdfs://node1a202:8020/hbase1
drwxr-xr-x - hbase hbase 0 2017-05-11 10:46 hdfs://node1a202:8020/hbase2
drwxr-xr-x - root supergroup 0 2016-12-01 17:30 hdfs://node1a202:8020/home
drwxr-xr-x - mdss supergroup 0 2016-12-13 18:30 hdfs://node1a202:8020/idfs
drwxr-xr-x - hdfs supergroup 0 2017-05-22 18:51 hdfs://node1a202:8020/system
drwxrwxrwt - hdfs supergroup 0 2017-05-31 17:37 hdfs://node1a202:8020/tmp
drwxrwxr-x+ - hdfs supergroup 0 2017-05-04 15:48 hdfs://node1a202:8020/user
在HADOOP.COM中进行相同的操作
2）运行distcp程序将IDC的数据复制到HADOOP集群，命令如下：
[root@node1a141 ~]# hadoop distcp hdfs://node1a141:8020/tmp/test.sh hdfs://node1a202:8020/tmp/
5 附录
两集群的/etc/krb5.conf完整文件内容如下：
[root@node1a141 IDC]# cat /etc/krb5.conf
[logging]
default = FILE:/var/log/krb5libs.log
kdc = FILE:/var/log/krb5kdc.log
admin_server = FILE:/var/log/kadmind.log
[libdefaults]
default_realm = IDC.COM
dns_lookup_realm = false
dns_lookup_kdc = false
ticket_lifetime = 7d
renew_lifetime = 30
forwardable = true
renewable=true
#default_ccache_name = KEYRING:persistent:%{uid}
[realms]
HADOOP.COM = {
kdc = node1a198
admin_server = node1a198
default_realm = HADOOP.COM
supported_enctypes = aes128-cts:normal des3-hmac-sha1:normal arcfour-hmac:normal camellia256-cts:normal camellia128-cts:normal des-hmac-sha1:normal des-cbc-md5:normal des-cbc-crc:normal
}
IDC.COM = {
kdc = node1a141
admin_server = node1a141
default_realm = IDC.COM
supported_enctypes = aes128-cts:normal des3-hmac-sha1:normal arcfour-hmac:normal camellia256-cts:normal camellia128-cts:normal des-hmac-sha1:normal des-cbc-md5:normal des-cbc-crc:normal
}
[domain_realm]
.hadoop.com=HADOOP.COM
hadoop.com=HADOOP.COM
.IDC.com=IDC.COM
IDC.com=IDC.COM
node1a141 = IDC.COM
node1a143 = IDC.COM
node1a210 = HADOOP.COM
node1a202 = HADOOP.COM
node1a203 = HADOOP.COM
[capaths]
IDC.COM = {
HADOOP.COM = .
}