Configuring Hive and Impala for high availability with Hue

To configure Hive for high availability with Hue, you must have two or more HiveServer2 roles. For Impala, you must have two or more Impala daemon (impalad) roles.

SSH network access to host machines with a HiveServer2 or Impala Daemon role.
External database configured for each H2S and Impala Daemon.
Hue Load Balancer Hive/Impala Load Balancer configured with Source IP Persistence.

Source IP Persistence

Without IP Persistence, you may encounter the error, “Results have expired, rerun the query if needed.

Hue supports High Availability through a "load balancer" to HiveServer2 and Impala. Because the underlying Hue thrift libraries reuse TCP connections in a pool, a single user session may not have the same TCP connection. If a TCP connection is balanced away from a HiveServer2 or Impalad instance, the user session and its queries (running or returned) can be lost and trigger the “Results have expired" error.

To prevent sessions from being lost, configure the Hive/Impala Load Balancer with Source IP Persistence so that each Hue instance sends all traffic to a single HiveServer2/Impala instance. Of course, this is not true load balancing, but a configuration for failover High Availability.

To prevent sessions from timing out while in use, add more Hue Server instances, so that each can be pinned to another HiveServer2/Impala instance. And for both HiveServer2/Impala, set the affinity timeout (that is, the timeout to close persisted sessions) to be longer than the impala query and session timeouts.

For the best load distribution, create multiple profiles in your load balancer, per port, for both non-Hue clients and Hue clients. Have non-Hue clients distribute loads in a round robin and configure Hue clients with source IP Persistence on dedicated ports, for example, 21000 for impala-shell, 21050 for impala-jdbc, and 21051 for Hue.

In Cloudera Manager, add roles for HiveServer2 and for Impala daemon:
1. Configure the cluster with at least two roles for HiveServer2:
  1. Go to the Hive service and select Actions > Add Role Instances.
  2. Click HiveServer2, assign one or more hosts, and click OK > Continue.
  3. Check each role and select Actions for Selected > Start and click Start.
2. Configure the cluster with at least two roles for Impala Daemon:
  1. Go to the Impala service and select Actions > Add Role Instances.
  2. Click Impala Daemon, assign one or more hosts, and click OK > Continue.
  3. Check each role and select Actions for Selected > Start and click Start.

Install a proxy service:

This is an example of how to add a proxy server for each HiveServer2 and Impala Daemon with multiple profiles using the open source TCP/HTTP load balancer, HAProxy.

Install HAProxy for your operating system:

yum install haproxy

apt-get install haproxy

zypper addrepo http://download.opensuse.org/repositories/server:http/SLE_12/server:http.repo
zypper refresh
zypper install haproxy

Configure HAProxy for each role, for example:

vi /etc/haproxy/haproxy.cfg

listen impala-shell
    bind :21001
    mode tcp
    option tcplog
    balance roundrobin
    stick-table type ip size 20k expire 5m
server impala_0 shortname-2.domain:21000 check
server impala_1 shortname-3.domain:21000 check

listen impala-jdbc
    bind :21051
    mode tcp
    option tcplog
    balance roundrobin
    stick-table type ip size 20k expire 5m
server impala_0 shortname-2.domain:21050 check
server impala_1 shortname-3.domain:21050 check

listen impala-hue
    bind :21052
    mode tcp
    option tcplog
    balance source
server impala_0 shortname-2.domain:21050 check
server impala_1 shortname-3.domain:21050 check

listen hiveserver2-jdbc
    bind :10001
    mode http
    option tcplog
    balance roundrobin
    stick-table type ip size 20k expire 5m
server hiveserver2_0 shortname-1.domain:10000 check
server hiveserver2_1 shortname-2.domain:10000 check

listen hiveserver2-hue
    bind :10002
    mode tcp
    option tcplog
    balance source
    stick-table type ip size 20k expire 5m
server hiveserver2_0 host shortname-1.domain:10000 check
server hiveserver2_1 host shortname-2.domain:10000 check

Replace shortname-#.domain with those in your environment:

sed -i "s/host shortname/your host shortname/g" /etc/haproxy/haproxy.cfg
sed -i "s/domain/your domain/g" /etc/haproxy/haproxy.cfg

Hue does not maintain any state for the connection to HS2. If Hue connects to one HS2 instance and the query is being executed on another HS2 instance in an HA setup, then commands including listing tables or databased could fail. Enabling a sticky session using stick table is used to avoid this issue.

When you specify stick-table type ip size 20k expire 5m, the stick table tracks the HTTP request rate of each client that passes through the load balancer.

The table's primary key is of the type ip, which implies that the keys are IP addresses
The table holds a maximum of 20 thousand records
A record expires after 5 minutes unless it is accessed during that time

Restart haproxy:
```
service haproxy restart
```
Run netstat to ensure your proxies are running:
```
netstat | grep LISTEN
```