Posts

PostgREST on RHEL 7.2

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PostgREST is an HTTP server written in Haskell that serves a fully RESTful API from a PostgreSQL database. It generates the endpoints directly from the database schema so you do not have to write anything from scratch. You just download the binary, fire it up with a database connection string and you are good to go.

You won't find it as a .deb or .rpm package at the time of writing, so you have to install it manually and create your own startup scripts.

In this post I will describe how to do this on a Redhat Enterprise Linux (RHEL 7.2) server in a managed SELinux context. The PostgreSQL database instance runs on the same server in this example.

Note that RHEL 7.2 ships with PostgreSQL 9.2 which is not supported by PostgREST so you have to upgrade to version 9.3 or later from the PostgreSQL repositories.

Download, install and test the binary  Download the tarball from the github repo. Select the Centos binary for compatibility with RHEL, then untar it and move it to a directory on …

Tomcat 8 on Debian Jessie with PSI Probe and OpenNMS to monitor performance (Part 3)

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We looked at Tomcat 8 in Part 1 of this series and at PSI Probe as a replacement for the default Tomcat Manager application in Part 2.

Now PSI Probe is great for managing Tomcat and its applications, but it does not actively generate alerts if Tomcat is in difficulty, or any other part of the application stack for that matter, so this is where OpenNMS plugs the gap.

Network Management with OpenNMS If you cut your teeth on the mainframes of the recent past, you will be familiar with network management tools like HP OpenView and IBM Tivoli. These tools are famous for their complexity and cost, so alternatives like Nagios (subsequently forked as Icinga) and OpenNMS emerged as open source alternatives.

OpenNMS is a Java-based, agentless monitoring tool that uses SNMP to monitor devices on the network. It was designed to manage service level agreements, so in addition to fault reporting (with trouble ticketing), it has a large number of service monitors to report against service threshold…

Tomcat 8 on Debian Jessie with PSI Probe and OpenNMS to monitor performance (Part 2)

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In Part 1 of this series of three, I looked at the installation of Tomcat 8 on Debian Jessie. The standard Tomcat Manager web application is limited in functionality, and the look-and-feel is distinctly lacking, so here is PSI Probe instead.

PSI Probe features PSI Probe supplements the basic functionality of Tomcat Manager with a number of very useful features, including:
real-time monitoring of request traffic on the Connectors, from any Remote IP, or per application;viewing of Data Source pool usage, and query execution;monitoring of Logs, with the ability to dynamically change log levels at runtime;viewing the Thread execution stack, with the option of killing threads;dashboards to monitor the JVM, showing memory usage, swap file usage and garbage collection control;and detailed System properties data. PSI Probe is a fork of an older application called Lambda Probe that was last updated in 2006. This is a Lambda Probe:


Installing PSI Probe You have to build PSI Probe from the source…

Tomcat 8 on Debian Jessie with PSI Probe and OpenNMS to monitor performance (Part 1)

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This is the first of three posts about the latest version of Apache Tomcat, still the most widely used application server, on Debian Jessie, with PSI Probe to manage it and OpenNMS to monitor its up-time.

What's new in Tomcat 8? Debian Jessie was released with Apache Tomcat 8, which provides the following:
Java Servlet 3.1, an incremental release of the servlet specification that includes non-blocking I/O to improve scaleability and an HTTP protocol upgrade mechanism that allows the client and the server to negotiate a transition from HTTP 1.1 to some other new chosen protocol;JavaServer Pages 2.3, a maintenance release to provide support for Expression Language (EL) 3.0 and to use the functionality of the Servlet 3.1 API; Java Unified Expression Language (EL) 3.0, which allows EL to run in a standalone mode outside of servlets or JSPs, plus lambda expressions and other Java 8 goodies;WebSocket 1.1, which allows full duplex communications over TCP so that bidirectional data can flo…

How to fix and run the broken EclipseLink Tutorial example (JSF and JPA)

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The EclipseLink Tutorial The EclipseLink implementation of JPA has a tutorial for running it with JSF on the Tomcat servlet container, instead of a full-blown Java EE Application Server.

The tutorial mentions two source code downloads, both of which were missing from the page, but I managed to find a directory of the stubbed tutorial source that you can use as a starting point as you follow the EclipseLink tutorial, as well as the code for the completed version of the application.

Unfortunately, the tutorial is out-of-date, the source code has several errors, and the application itself is very primitive, but you may be curious enough to want to try it out anyway. This is how to get the completed application running on Tomcat against a PostgreSQL database using the Eclipse IDE.

The application is a very simple Order application with this object model:

Set up the environment Download and unzip the code for the completed version of the application. It is an Ant project that is not…

Upgrade to Debian Jessie before the Official release date

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I have been running Gnome Classic on Debian Wheezy for the last couple of years, but Debian Jessie will be released soon and it includes some interesting new packages:
Docker for Linux containersSteam for gaming (in non-free) ownCloud for private cloud storage systemd as default, which caused a lot of angst in the Debian community Unlike other distros, the Debian release policy is to release when it is good and ready. Jessie was frozen in November last year and the package maintainers are down to the last 55 Release Critical bugs, so Jessie is likely to be formally released in April this year.

None of my systems are mission-critical so I decided to do an in-place upgrade from Wheezy to Jessie now, before it is officially released.


It's all very straightforward if you follow the Debian instructions.

First, back up the data you care about to an external drive in the unlikely event that it all goes pear-shaped. You do backup regularly don't you? Good for you. I don't. Nobody …

Lightweight web-based transactional systems

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Reanimating a legacy system I have a set of data from an old legacy application that must be resurrected and web-enabled. The data was extracted from a relational database so it is structured in a conventional third-normal form, but the original application was pensioned off a long time ago, and probably a good thing too.
The user interface and its business logic must be rebuilt as a web-based transactional application so that the data can be accessible from a variety of devices, so I had to decide on a technology stack, but how? There are dozens of database systems, hundreds of software languages, scores of web-development frameworks, and more opinions about the matter than there are trolls on 9GAG.

The formal approach to making a decision would be to consider all the various technologies at each layer of the application stack and then weigh up the pros and cons of each.
A less formal approach would be to ask someone who has done this sort of thing before, like a grizzled Unix veter…