Poni v0.5-4-g6e6a332 documentation

Modifying Properties and Settings

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Modifying Properties and Settings


Although these examples use the set command, the functionality is mostly the same for the settings set command and for the extra variable arguments of the script command.

Properties vs. Settings

Each node and system has their own set of “properties”. Some of the properties have special behavior as described in the System and Node Property Reference.

Properties are stored internally in the Poni repository as JSON and all data-types and structures supported by JSON can be used in Poni. Hierarchies of properties can be created and accessed with the dot-syntax, e.g. poni set somenode server.http.port:int=80 or $node.server.http.port in Cheetah templates.

The repository JSON storage format is kept sorted by key and pretty-printed for readability especially when using a version control system to store the repository:

$ poni add-node example
$ poni set example server.http.port:int=80 server.http.interface=
$ cat ~/.poni/default/system/example/node.json
    "host": "",
    "server": {
        "http": {
            "interface": "",
            "port": 80

Example version control diff:

$ poni vc checkpoint baseline
$ poni set example server.http.port:int=8080
$ poni vc diff
diff --git a/system/example/node.json b/system/example/node.json
index ae0a8f4..4e86c5d 100644
--- a/system/example/node.json
+++ b/system/example/node.json
@@ -3,7 +3,7 @@
     "server": {
         "http": {
             "interface": "",
-            "port": 80
+            "port": 8080
\ No newline at end of file

Properties are for storing node/system-specific information that is not e.g. inherited automatically from parent-nodes. However, when adding nodes with the add-node command, their properties can be copied (once) from the parent node with the --copy-props switch.


Properties currently do not support explicit typing or validation schemas: any data-types can be used, but they are not actively verified.

Settings are config-specific repositories and share the same structure and storage format with properties. However, config settings have a bit more features, namely inheritance and type validation.

Settings Type Validation


Settings Inheritance


Setting Basic Node and System String Properties

It is often necessary to set some basic node properties, such as the hostname or the IP-address:

$ poni list -p
    node  webshop/frontend/server1
    prop      depth:3, host:'', index:0
    node  webshop/frontend/server2
    prop      depth:3, host:'', index:1
$ poni set -v server1 host=www.google.com
root  INFO    webshop/frontend/server1: set host=u'www.google.com' (was u'')
$ poni set -v server2 host=www.amazon.com
root  INFO    webshop/frontend/server2: set host=u'www.amazon.com' (was u'')

In the above example setting string properties is done by using the form name=value. The -v or --verbose flag enables every change made to be printed out.


Internally string properties are stored in Unicode form and the u before the values in the above output indicate this.

Setting Integer, Float, Boolean Data-types

Other data-types can be specified by adding a colon and the type after the property name:

$ poni set -v server1 foo:int=123 bar:float=456.7 baz:bool=true
root  INFO    webshop/frontend/server1: set baz=True (was None)
root  INFO    webshop/frontend/server1: set foo=123 (was None)
root  INFO    webshop/frontend/server1: set bar=456.69999999999999 (was None)

Integer values can be specified in binary, octal, decimal or hexdecimal format:

$ poni set -v server2 a:int=0b1010 b:int=0o644 c:int=0xff
root  INFO    webshop/frontend/server2: set a=10 (was None)
root  INFO    webshop/frontend/server2: set c=255 (was None)
root  INFO    webshop/frontend/server2: set b=420 (was None)

Integer or float values can optionally specify SI (base-10) or IEEE-1541 (base-2) multipliers:

$ poni set -v server2 max_mem:int=64Mi disk_space:int=100Gi network_speed:int=100M
root  INFO    webshop/frontend/server2: set disk_space=107374182400 (was None)
root  INFO    webshop/frontend/server2: set network_speed=100000000 (was None)
root  INFO    webshop/frontend/server2: set max_mem=67108864 (was None)

Null values

A null value (None in Python) can be set with null as the data type:

$ poni set -v server2 nothing:null    INFO    webshop/frontend/server2: set nothing=None (no change)

Eval expressions

Simple Python-expressions can be evaluated using the eval conversion:

$ poni set -v server2 meaning:eval=21*6/3
root  INFO    webshop/frontend/server2: set meaning=42 (was None)

$ poni set -v server2 'msglen:eval=len("hello, world")'
root  INFO    webshop/frontend/server2: set msglen=12 (was None)

Accessing Environment Variables

Enviroment variables can be stored as properties using the env conversion:

$ poni set server2 -v term:env=TERM shell:env=SHELL
root  INFO    webshop/frontend/server2: set term=u'xterm-color' (was None)
root  INFO    webshop/frontend/server2: set shell=u'/bin/bash' (was None)

Resolving IP Addresses

Resolving DNS names to IPv4 or IPv6 addresses:

$ poni set -v server2 address1:ipv4=www.funet.fi address2:ipv6=www.funet.fi
root  INFO    webshop/frontend/server2: set address1=u'' (was None)
root  INFO    webshop/frontend/server2: set address2=u'2a00:16a0:0:100::21:3' (was None)


Currently only the first available IP address is returned. If there are more than one IPs, the rest are just discarded. Also note that resolving the address is done only once (during the set command) and not updated automatically.

Two-way Conversions

Many conversions can be done in two ways: “to format X” (encoding) and “from format X” (decoding). Let’s use hex encoding strings as the example:

$ poni set server2 -v message:hex=hello
root  INFO    webshop/frontend/server2: set message='68656c6c6f' (was None)

I the above example the default direction, which is to encode, was used and “hello” was converted to its hexadecimal representation. In order to specify decoding instead of encoding, a minus-sign is added before the conversion name:

$ poni set server2 -v message:-hex=68656c6c6f
root  INFO    webshop/frontend/server2: set message='hello' (was u'68656c6c6f')

A plus-sign can be added in a similar fashion to explicitly define that encoding is requested, but it is redundant as the default is always to encode.

Python standard codec names (see http://docs.python.org/library/codecs.html#standard-encodings) can be used in conversions, for example:

$ poni set server2 -v secret:rot13=confidential example:base64=hello123
root  INFO    webshop/frontend/server2: set secret='pbasvqragvny' (was None)
root  INFO    webshop/frontend/server2: set example='aGVsbG8xMjM=\n' (was None)

Character Set Conversions


Accessing Node Properties

Referencing node properties (set command) or config properties (set or settings set commands) is available thru the prop directive. To copy an existing property:

$ poni set -v server2 host2:prop=node.host
root  INFO    webshop/frontend/server2: set host2=u'www.amazon.com' (was None)

Chaining conversions

Multiple conversions can be chained together by adding more conversion separated by colons. For example, updating the private.ip node property by resolving the IP address of each host:

$ poni add-node linux/debian
$ poni add-node linux/ubuntu
$ poni set linux/debian host=www.debian.org
$ poni set linux/ubuntu host=www.ubuntu.org
$ poni set -v linux/ private.ip:prop:ipv4=node.host
root  INFO    linux/debian: set private.ip=u'' (was None)
root  INFO    linux/ubuntu: set private.ip=u'' (was None)

The funky part is the private.ip:prop:ipv4=node.host property definition. Let’s break it into parts:

  • private.ip defines the property we are overwriting
  • There are two conversions: prop and ipv4 (in that order!)
  • The starting value is a string containing the characters: node.host

Here’s how the whole thing gets processed for the linux/debian node:

  1. The string value node.host is fed to the prop conversion, which looks up the host property of the node object, which results in the value www.debian.org.
  2. The string value www.debian.org is given to the ipv4 conversion, which then tries to resolve the IP address behind it. The result is
  3. Finally, the value is stored into the private.ip node property.

Encoding and Decoding JSON

Data can be converted to and front JSON using the json conversion. For example, to decode a JSON input string and store the resulting object we can do something like this:

$ poni set server2 -v 'json_example:-json=[1, 2.3, "hello"]'
root  INFO    webshop/frontend/server2: set json_example=[1, 2.2999999999999998, u'hello'] (was None)

Note the minus-sign before json, indicating the decoding from JSON is requested. Encoding the sample input string to JSON (plus-sign) results in just wrapping the input string into a JSON string by adding one more level of quotes:

$ poni set server2 -v 'json_example2:+json=[1, 2.3, "hello"]'
root  INFO    webshop/frontend/server2: set json_example2='"[1, 2.3, \\"hello\\"]"' (was None)

Creating and Setting UUIDs

Conversion uuid4 can be used to create new totally random UUID:

$ poni set server -v nodeid:uuid4
root  INFO    webshop/frontend/server1: set nodeid=u'38c7363d-9fec-49d0-a1a0-913715caa04b' (was None)
root  INFO    webshop/frontend/server2: set nodeid=u'34075320-2b84-412d-8034-f45017edf7f4' (was None)

Converting a 16-byte string into UUID format:

$ poni set server1 -v sampleid:uuid=0123456789abcdef
root  INFO    webshop/frontend/server1: set sampleid=u'30313233-3435-3637-3839-616263646566' (was None)

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