This section applies to Virtuoso as of version 6.x and higher.
This documentation details how to configure the Subordinate (also called Slave) Nodes of a Virtuoso Elastic Cluster to service HTTP clients.
By default, only the Primary (also called Master) instance of a Virtuoso Elastic Cluster is configured to provide HTTP services.
The Subordinate (also called Slave) nodes of the cluster may also be configured to provide HTTP services, enabling load balancing by spreading HTTP requests across the cluster's nodes.
This documentation details the steps for the installation and configuration of a Virtuoso Elastic Cluster on Unix:
: Set up each instance as a HTTP Server;
: Install and configure HTTP services on each instance;
: Configure load balancing.
Step 1 : Set up each instance as a HTTP Server
Each node can be configured to provide HTTP services as follows:
[HTTP Server]section from the Primary instance's configuration file (by default,
virtuoso.ini) to the configuration file of each Subordinate instance:
[HTTPServer] ServerPort = 8890 ServerRoot = ../vsp DavRoot = DAV EnabledDavVSP = 0 HTTPProxyEnabled = 0 TempASPXDir = 0 DefaultMailServer = localhost:25 MaxClientConnections = 5 MaxKeepAlives = 10 KeepAliveTimeout = 10 MaxCachedProxyConnections = 10 ProxyConnectionCacheTimeout = 15 HTTPThreadSize = 280000 HttpPrintWarningsInOutput = 0 Charset = UTF-8 ;HTTPLogFile = logs/http.log MaintenancePage = atomic.html EnabledGzipContent = 1
ServerPortparameter to make it unique on the machine hosting this instance; i.e., if a subordinate instance is running on same physical node as the primary instance, then the subordinate's HTTP port must to be changed (from 8890, for instance) to a unique port (e.g., 8891).
Install the Virtuoso Conductor to enable HTTP Administration of the instance being configured. Note: if the subordinate instance is not on the same machine as the primary instance, then the vad directory may also need to be copied from the primary instance to the subordinate instance.:
SQL> vad_install ('../vad/conductor_dav.vad', 0); SQL_STATE SQL_MESSAGE VARCHAR VARCHAR _______________________________________________________________________________ 00000 No errors detected 00000 Installation of "Virtuoso Conductor" is complete. 00000 Now making a final checkpoint. 00000 Final checkpoint is made. 00000 SUCCESS 6 Rows. -- 10263 msec. SQL>
Step 2 : Install and configure HTTP services on each instance
Any HTTP services required on the subordinate instance will need
to specifically installed or configured on that physical node. For
example, the Virtuoso default SPARQL endpoint (
/sparql ) may be configured by:
Log in into the Virtuoso Conductor http://hostname:port/conductor :
Go the the Web Application Server -> Virtual Domains & Directories tab:
Select the New Directory Action for the Default Web Site HTTP host:
Select the Type radio button and SPARQL access point item from the drop down list box:
Enter /sparql as the Path param in the Virtual Directory Information section and click Save Changes:
The SPARQL endpoint will not be accessible on http://hostname:port/sparql the the newly configured slave nodes:
Further details on SPARQL endpoint configuration can be found in Service Endpoint documentation section.
Typical Virtuoso server log output from a slave node when started, showing the HTTP server running on port 8890, being:
20:12:49 OpenLink Virtuoso Universal Server 20:12:49 Version 07.10.3209-pthreads for Linux as of Apr 26 2014 20:12:49 uses parts of OpenSSL, PCRE, Html Tidy 20:12:49 Registered to OpenLink Virtuoso (Internal Use) 20:12:49 Personal Edition license for 500 connections 20:12:49 Issued by OpenLink Software 20:12:49 This license will expire on Sun May 17 06:18:35 2015 GMT 20:12:49 Enabled Cluster Extension 20:12:49 Enabled Column Store Extension 20:12:57 Database version 3126 20:12:57 SQL Optimizer enabled (max 1000 layouts) 20:12:58 Compiler unit is timed at 0.000208 msec 20:12:58 Roll forward started 20:12:58 Roll forward complete 20:12:59 Checkpoint started 20:12:59 Checkpoint finished, log reused 20:12:59 HTTP/WebDAV server online at 8890 20:12:59 Server online at 12202 (pid 15969)
Step 3 : Configure load balancing
A reverse-proxy service (like Nginx or Apache) can then be configured such that requests are proxied across as any or all nodes of the cluster, to provide the desired load balancing.
Only the Primary Node of an Elastic Cluster may be configured as a Publisher for Virtuoso Replication Cluster purposes.
The Virtuoso 500 billion triple Berlin SPARQL Benchmark (BSBM) dataset runs were performed on a 24-node Elastic Cluster. Each node was configured to provide HTTP services and a SPARQL endpoint, and the query load was spread over the entire cluster.