- Sites, Services, service endpoints, and Service Groups can be extended by adding custom key-value pairs (this follows the GLUE2 extensibility mechanism).
- Extension properties address a number of use cases, such as filtering Sites and/or Services that define particular properties.
- Selected methods in the Configuration Database API support the ’extensions' URL parameter. This parameter is used to filter resources according to the extensions they define (described below).
- Properties are rendered in the XML results of the Site/Service/ServiceGroup using the “EXTENSIONS” XML element, for an example see a sample output from get_service_endpoint(link to old EGI Wiki)
- Note, anyone with permissions over the target entity can add extension properties to that object.
- This allows ‘Folksonomy’ building: ‘a user-generated system of classifying and organizing content into different categories by the use of metadata such as electronic tags’
- A number of use cases can be addressed; e.g. filtering Sites that support a specific property, e.g. ‘P4U_Pilot_Cloud_Wall’
- Key-value pairs prevent certain characters from being used in their values. This includes the equals and opening/closing parenthesis chars ‘=()’. This is to simplify lexical parsing of the query. In addition, to guard against cross-site scripting attacks, the quote, double quote, semi-colon and back tick chars are also not allowed.
- Keys must be unique for a given site, service, or service endpoint, or service group.
Extension Properties in the PI
- Selected PI methods allow results to be filtered by extension properties via the ’extensions’ PI parameter.
- Supported methods include: get_site, get_site_list, get_service_endpoints and get_service_group, get_downtime, get_downtime_nested, get_site_list.
- For individual method support please refer to the PI documentation: GOCDB/PI/Technical Documentation (link to old EGI Wiki)
- The format of the ’extensions’ PI parameter is one or more (key=value) pairs
enclosed in brackets.
- The value part of a (k=v) pair can be ommitted if filtering by value is not required (i.e. ‘(somekey=)’ means select all resources that define the ‘somekey’ property with any value.
- (k=v) pairs can be optionally prefixed with one of following operators: AND, OR, NOT.
- If no operator is specified before the FIRST (k=v) pair, then AND is assumed.
- A single operator applies to ALL the (k=v) pairs to the right of the operator until another operator is encountered.
- An AND forms a logical conjunction with any previously specified conditions.
- An OR forms a logical disjunction with any previously specified conditions.
- A NOT forms a logical conjunction with any previously specified conditions (it can be read as ‘AND NOT’)
- Because an OR always forms a logical disjunction with any previously specified conditions, you can’t OR against a group occurring to the right that contains multiple k=v pairs e.g. the following is not supported (if there is sufficient demand, it could be considered for a future enhancement): - ((k=v1)AND(k=v2)) OR ((k=v3)AND(k=v4))
- Eg (note no leading AND):
- (key1=val)(key2=va2)OR(key3=val3)(key4=val4)NOT(key5=val5)(key6=val6) is expanded to:
- AND(key1=val)AND(key2=va2)OR(key3=val3)OR(key4=val4)NOT(key5=val5)NOT(key6=val6) which is interpreted as:
- (((key1=val)AND(key2=va2))OR(key3=val3)) OR(key4=val4) NOT(key5=val5) NOT(key6=val6)
- (VObing=true)AND(VObaz=true)AND(VObar=true)OR(s1p1=v1) is equal to:
- (VO=food)OR(VO2=bar)AND(s4p1=v1) is equal to:
- (VO=food)(s4p1=v1)OR(VObar=true)(VObaz=true) is equal to:
- (VO=food)(s4p1=v1)OR(VObaz=true)AND(VObling=true) is equal to:
To return all sites that define VO with a value of Alice:
Use no value to define a wildcard search, i.e. all sites that define the VO property regardless of value:
NOTE: From version 5.7 (Autumn/Winter 2016) keys must be unique for a given site, service, or service endpoint, or service group. The following section of documentation has not yet been changed to reflect this.
Extensions also supports OR/AND/NOT operators. This can be used to search against multiple key values eg:
These can be used together:
When no operator is specified the default is AND, therefore the following:
Is the same as:
The extensions parameter can also be used in conjunction with the existing parameters previously supported:
The site_extensions and service_extensions can also be used on the get_downtime and get_downtime_nested_services methods using same logic described above. Note, the EXTENSIONS element is not rendered in the XML output for these queries.
Standard Extension Properties
For EGI Services, the Standard Extension property “HostDN” has been defined to allow the fetching the DNs of multiple hosts behind a load balanced service from the endpoint properties of a single GOCDB Service, rather than creating multiple GOCDB Services with different host DNs.
To supply multiple or alternate DN(s) for a service, for example of the multiple hosts supporting a single service entry, the Service Extension Property (hereafter Ext) “HostDN” SHOULD be used. If Ext “HostDN” is present it MUST contain one or more x.509 DN values. Multiple values MUST be delimited by enclosing each within “<>” characters. If Ext “HostDN” is present, the Service “Host DN” SHOULD contain the x.509 SubjectAltName used in the X509 certificate(s) presented by the hosts identified by the Ext “HostDN” values.