Moments of clarity in code

Discoveries in doings things right

[mmajiscode]

Chef server rabbitmq trouble with Ubuntu 12.04.1 (Bunny::ProtocolError)

It seems there's a few steps missing from the Chef server packaging on Ubuntu 12.04.1. The user for RabbitMQ is not created etc.

Error:

merb : chef-server (api) : worker (port 4000) ~ Connection failed - user: chef - (Bunny::ProtocolError)

Jonathan Polansky to the rescue with the following:

# rabbitmqctl add_vhost /chef # rabbitmqctl add_user chef  # rabbitmqctl set_permissions -p /chef chef ".*" ".*" ".*"

Thanks! :)

EDIT: I believe this is actually due to changes in hostname between restarts on EC2. Ubuntu requests host-name (and domain-name) from DHCP and EC2 provides changing values at least for hostname. RabbitMQ in turn stores configuration in a directory named after the hostname. So after a restart and a hostname change, RabbitMQ configuration gets reset.

To make the settings stick, I edited the request statement in /etc/dhcp/dhclient.conf:

# REMOVED domain-name and host-name from the request list!

request subnet-mask, broadcast-address, time-offset, routers, 

        domain-name-servers, domain-search,

        netbios-name-servers, netbios-scope, interface-mtu,

        rfc3442-classless-static-routes, ntp-servers,

        dhcp6.domain-search, dhcp6.fqdn,

        dhcp6.name-servers, dhcp6.sntp-servers;

[mmajiscode]

Report EC2 instance id as a ganglia metric

EC2 instances provide metadata via http://169.254.169.254/latest/meta-data. Here's a oneliner to fetch the instance id of a running EC2 instance and supply it to Ganglia as a custom metric.

gmetric --name=vmInstanceId --value=`wget -q -O - http://169.254.169.254/latest/meta-data/instance-id || die \"wget instance-id has failed: $?\"` --type=string --slope=zero --tmax=0 --dmax=0

The wget part is flatteringly imitated from this Stackoverflow post.

[mmajiscode]

Ganglia gmetad summary data is not averaged

The data available in METRICS elements from Ganglia gmetad XML output with parameter /?filter=summary is, as suggested by the attribute name SUM instead of VAL, a sum of metric values for each host in a cluster or grid. 

The number of values in the SUM is given separately in the NUM attribute of each METRICS element. This may be different from the total number of running hosts (see HOSTS element) if not all hosts supply the given metric.

The calculation of averages is left as an exercise to the reader :)

[mmajiscode]

Activiti business rule task ruleVariablesInput syntax

The Activiti business rule task is defined like so:

<businessRuleTask id="businessRuleTask" activiti:ruleVariablesInput="${order}" activiti:resultVariable="rulesOutput" />

The activiti:ruleVariablesInput attribute takes UEL expression values while activiti:resultVariable takes a string value. Not using expressions (e.g. using only activiti:ruleVariablesInput="order") for the former will input a simple string to the rule engine instead of any Activiti process variable by the name "order".

Reading is hard. Time spent: 2 hours.

[mmajiscode]

Ganglia XML slope attribute

The slope="zero|positive|negative|both" attribute in ganglia metrics is meant to indicate the slope for the lifetime of the metric. 

The values for slope appear to denote the following:

zero - the metric value will never change

positive - the metric value will always increase or stay the same

negative - the metric value will always decrease or stay the same

both - the metric value can increase or decrease

The slope is used as a hint by gmetad for efficient use of RRDtool to store the metric data. A positive slope means gmetad will use RRDtool storage type COUNTER, which stores the difference between the previous and current values. Other slope values will use storage type GAUGE, which stores each actual metric value.

So. It's not an indication of the current slope of the metric.

http://sourceforge.net/apps/trac/ganglia/wiki/ganglia_readme http://ganglia.info/?tag=2-5-0 http://oss.oetiker.ch/rrdtool/tut/rrd-beginners.en.html 

[mmajiscode]

Ganglia gmetad interactive port XML queries

Ganglia developers appear not to have wasted too much time on documentation. Very little time at all, in fact.

The possible query strings to send to the gmetad interactive port (default 8652) are:

/?filter=summary (returns a summary of the whole grid, i.e. all clusters)

/cluster name (returns raw data of a cluster called "cluster name")

/cluster name/host name (returns raw data for host "host name" in cluster "cluster name")

/cluster name?filter=summary (returns a summary of only cluster "my cluster")

[mmajiscode]

How to specify custom bindings for DTD based code generation with JAXB2?

Don't. Convert the DTD to XSD using e.g. Trang.

[mmajiscode]

The markup declarations contained or pointed to by the document type declaration must be well-formed.

Some DTD validators give this cryptic error when the DTD contains the

<!DOCTYPE name [  .. >]

processing instruction (internal DTD) but does not contain XML markup.

To fix it, remove the parts above and refer to the DTD as external from XML documents. See http://xmlwriter.net/xml_guide/doctype_declaration.shtml

Better yet, don't use DTDs at all :)