# Ruby Scripting in NiFi Today I was asked about an issue that I didn't know how to
solve using NiFi. On the surface it sounded simple; just map an attribute to
another value. The attribute to map was 'port' and based on the port number
just add an attribute to more easily identify the system downstream. E.g. for
port 10003; syslog:local, for 10004; syslog:db1, etc. After a bit of digging I
found a few different options to solve this. ## Many UpdateAttribute Processors The first is to create a new UpdateAttribute processor for
each incoming stream. This labels (places an attribute) on all files that come
in from that listener. It looked like this:  This looks a bit confusing and tedious but is very precise
and arguably easier to read, especially when we label the processors. It also
has the added advantage of not having to change the port in more than one
place. If for example, the local logs coming in over port 10002 need to change
to port 10003, then we just make that change in the ListenSyslog processor and
the rest remains unchanged. ## One UpdateAttribute Using the Advanced The advanced option allowed me to keep all the configuration
in one place, easily mapping port numbers to tags. The two disadvantages I ran
into were: 1. A fairly tedious process to get each mapping. It
involved: * Create new rule * Add name * Search for existing
rule to import * Change port number
and associated label 2. Must now change the port in two different places if it
were to change I would look like:  ## ExecuteScript Processor This again allows me to keep all the configuration in one
place and makes it much easier to make changes. I created a processor that stores the mappings in a hash and
adds the correct attribute appropriately. It looks like so:  From the UI perspective it looks very similar to the single
UpdateAttribute solution. This requires the addition of the script: {% highlight ruby %} map = { 10 =>
"system1", 9 =>
"system2", 8 =>
"system3", } map.default = "unknown" flowFile = session.get() return unless flowFile label = map[flowFile.getAttribute("port")] flowFile = session.putAttribute(flowFile,
"system", label) session.transfer(flowFile, REL_SUCCESS) session.commit() {% endhighlight %} It is more complex by adding the need to understand a
scripting language and also doesn't remove the requirement of changing the port
number in more than one place. The script can add more complexity if it becomes
necessary to reference as a file rather than using the 'Script Body' option in
the processor. The main advantage is that it makes it easier to change the
mapping - just copy and paste one of the lines of the hash and make changes all
in one place. Given NiFi's goal of minimising the need for data flow
managers to know how to code, it's unlikely this is the best approach. # Conclusion The first option is quite foreign to programmers who feel
like it isn't generic. This is understandable given that it does feel a bit
like copy and paste. I would say it is the most NiFi way of achieving the
mapping as it is the solution which is most self-describing and resistant to
change.
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