High Availability

Configure Knox instances

All Knox instances must be synced to use the same topologies credentials keystores. These files are located under {GATEWAY_HOME}/conf/security/keystores/{TOPOLOGY_NAME}-credentials.jceks. They are generated after the first topology deployment. Currently these files can be synced just manually. There is no automation tool. Here are the steps to sync topologies credentials keystores:

  1. Choose Knox instance that will be the source for topologies credentials keystores. Let's call it keystores master
  2. Replace topologies credentials keystores in the other Knox instance with topologies credentials keystores from keystores master
  3. Restart Knox instances

High Availability with Apache HTTP Server + mod_proxy + mod_proxy_balancer

1 - Requirements

openssl-devel is required for Apache Module mod_ssl.

sudo yum install openssl-devel
Apache HTTP Server

Apache HTTP Server 2.4.6 or later is required. See this document for installing and setting up Apache HTTP Server: http://httpd.apache.org/docs/2.4/install.html

Hint: pass --enable-ssl to ./configure command to enable Apache Module mod_ssl generation.

Apache Module mod_proxy

See this document for setting up Apache Module mod_proxy: http://httpd.apache.org/docs/2.4/mod/mod_proxy.html

Apache Module mod_proxy_balancer

See this document for setting up Apache Module mod_proxy_balancer: http://httpd.apache.org/docs/2.4/mod/mod_proxy_balancer.html

Apache Module mod_ssl

See this document for setting up Apache Module mod_ssl: http://httpd.apache.org/docs/2.4/mod/mod_ssl.html

2 - Configuration example
Generate certificate for Apache HTTP Server

See this document for an example: http://www.akadia.com/services/ssh_test_certificate.html

By convention, Apache HTTP Server and Knox certificates are put into /etc/apache2/ssl/ folder.

Update Apache HTTP Server configuration file

This file is located under {APACHE_HOME}/conf/httpd.conf.

Following directives have to be added or uncommented in the configuration file:

  • LoadModule proxy_module modules/mod_proxy.so
  • LoadModule proxy_http_module modules/mod_proxy_http.so
  • LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
  • LoadModule ssl_module modules/mod_ssl.so
  • LoadModule lbmethod_byrequests_module modules/mod_lbmethod_byrequests.so
  • LoadModule lbmethod_bytraffic_module modules/mod_lbmethod_bytraffic.so
  • LoadModule lbmethod_bybusyness_module modules/mod_lbmethod_bybusyness.so
  • LoadModule lbmethod_heartbeat_module modules/mod_lbmethod_heartbeat.so
  • LoadModule slotmem_shm_module modules/mod_slotmem_shm.so

Also following lines have to be added to file. Replace placeholders (${...}) with real data:

Listen 443
<VirtualHost *:443>
   SSLEngine On
   SSLProxyEngine On

   ProxyRequests Off
   ProxyPreserveHost Off

   <Proxy balancer://mycluster>
     BalancerMember ${HOST_#1} route=1
     BalancerMember ${HOST_#2} route=2
     BalancerMember ${HOST_#N} route=N

     ProxySet failontimeout=On lbmethod=${LB_METHOD} stickysession=ROUTEID 

   ProxyPass / balancer://mycluster/
   ProxyPassReverse / balancer://mycluster/


  • SSLProxyEngine enables SSL between Apache HTTP Server and Knox instances;
  • SSLCertificateFile and SSLCertificateKeyFile have to point to certificate data of Apache HTTP Server. User will use this certificate for communications with Apache HTTP Server;
  • SSLProxyCACertificateFile has to point to Knox certificates.
Start/stop Apache HTTP Server
APACHE_HOME/bin/apachectl -k start
APACHE_HOME/bin/apachectl -k stop

Use Knox samples.