PuppetDB 1.1 » API » Query Tutorial

This page is a walkthrough for constructing several types of PuppetDB queries. It uses the version 2 API in all of its examples; however, most of the general principles are also applicable to the version 1 API.

If you need to use the v1 API, note that it lacks many of v2’s capabilities, and be sure to consult the v1 endpoint references before attempting to use these examples with it.

How to query

Queries are performed by performing a GET request to an endpoint URL and supplying a querystring parameter called query, which contains the query to execute. Results are always returned in application/json form. A curl command like the following can be used to easily try queries from the command line:

curl -H 'Accept: application/json' -X GET http://puppetdb:8080/v2/<resources-or-facts> --data-urlencode query@<filename>

where filename contains the query to execute.

Resources Walkthrough

Our first query

Let’s start by taking a look at a simple resource query. Suppose we want to find the user “nick” on every node. We can use this query:

["and",
  ["=", "type", "User"],
  ["=", "title", "nick"]]

This query has two "=" clauses, which both must be true.

In general, the "=" operator follows a specific structure:

["=", <attribute to compare>, <value>]

In this case, the attributes are “type” and “title”, and the values are “User” and “nick”.

The "and" operator also has a well-defined structure:

["and", <query clause>, <query clause>, <query clause>, ...]

The query clauses can be any legal query (including another "and"). At least one clause has to be specified, and all the clauses have to be true for the "and" clause to be true. An "or" operator is also available, which looks just like the "and" operator, except that, as you’d expect, it’s true if any specified clause is true.

The query format is declarative; it describes conditions the results must satisfy, not how to find them. So the order of the clauses is irrelevant. Either the type clause or the title clause could come first, without affecting the performance or the results of the query.

If we execute this query against the /resources route, we get results that look something like this:

[{
  "parameters" : {
    "comment" : "Nick Lewis",
    "uid" : "1115",
    "shell" : "/bin/bash",
    "managehome" : false,
    "gid" : "allstaff",
    "home" : "/home/nick",
    "groups" : "developers",
    "ensure" : "present"
  },
  "sourceline" : 111,
  "sourcefile" : "/etc/puppet/manifests/user.pp",
  "exported" : false,
  "tags" : [ "firewall", "default", "node", "nick", "role::base", "users", "virtual", "user", "account", "base", "role::firewall::office", "role", "role::firewall", "class", "account::user", "office", "virtual::users", "allstaff" ],
  "title" : "nick",
  "type" : "User",
  "resource" : "0ae7e1230e4d540caa451d0ade2424f316bfbf39",
  "certname" : "foo.example.com"
}]

Our results are an array of “resources”, where each resource is an object with a particular set of keys.

parameters: this field is itself an object, containing all the parameters and values of the resource sourceline: the line the resource was declared on sourcefile: the file the resource was specified in exported: true if the resource was exported by this node, or false otherwise tags: all the tags on the resource title: the resource title type: the resource type resources: this is an internal identifier for the resource used by PuppetDB certname: the node that the resource came from

There will be an entry in the list for every resource. A resource is specific to a single node, so if the resource is on 100 nodes, there will be 100 copies of the resource (each with at least a different certname field).

Excluding results

We know this instance of the user “nick” is defined on line 111 of /etc/puppet/manifests/user.pp. What if we want to check whether or not we define the same resource somewhere else? After all, if we’re repeating ourselves, something may be wrong! Fortunately, there’s an operator to help us:

["and",
  ["=", "type", "User"],
  ["=", "title", "nick"],
  ["not",
    ["and",
      ["=", "sourceline", "/etc/puppet/manifests/user.pp"],
      ["=", "sourcefile", 111]]]]

The "not" operator wraps another clause, and returns results for which the clause is not true. In this case, we want resources which aren’t defined on line 111 of /etc/puppet/manifests/user.pp.

Resource attributes

So far we’ve seen that we can query for resources based on their certname, type, title, sourcefile, and sourceline. There are a few more available:

["and",
  ["=", "tag", "foo"],
  ["=", "exported", true],
  ["=", ["parameter", "ensure"], "present"]]

This query returns resources whose set of tags contains the tag “foo”, and which are exported, and whose “ensure” parameter is “present”. Because the parameter name can take any value (including that of another attribute), it must be namespaced using ["parameter", <parameter name>].

The full set of queryable attributes can be found in the resource endpoint documentation for easy reference.

Regular expressions

What if we want to restrict our results to a certain subset of nodes? Certainly, we could do something like:

["or",
  ["=", "certname", "www1.example.com"],
  ["=", "certname", "www2.example.com"],
  ["=", "certname", "www3.example.com"]]

And this works great if we know exactly the set of nodes we want. But what if we want all the ‘www’ servers, regardless of how many we have? In this case, we can use the regular expression match operator ~:

["~", "certname", "www\\d+\\.example\\.com"]

Notice that, because our regular expression is specified inside a string, the backslash characters must be escaped. The rules for which constructs can be used in the regexp depend on which database is in use, so common features should be used for interoperability. The regexp operator can be used on every field of resources except for parameters, and exported.

Facts Walkthrough

In addition to resources, we can also query for facts. This looks similar, though the available fields and operators are a bit different. Some things are the same, though. For instance, support you want all the facts for a certain node:

["=", "certname", "foo.example.com"]

This gives results that look something like this:

[ {
  "certname" : "foo.example.com",
  "name" : "architecture",
  "value" : "amd64"
}, {
  "certname" : "foo.example.com",
  "name" : "fqdn",
  "value" : "foo.example.com"
}, {
  "certname" : "foo.example.com",
  "name" : "hostname",
  "value" : "foo"
}, {
  "certname" : "foo.example.com",
  "name" : "ipaddress",
  "value" : "192.168.100.102"
}, {
  "certname" : "foo.example.com",
  "name" : "kernel",
  "value" : "Linux"
}, {
  "certname" : "foo.example.com",
  "name" : "kernelversion",
  "value" : "2.6.32"
} ]

Fact attributes

In the last query, we saw that a “fact” consists of a “certname”, a “name”, and a “value”. As you might expect, we can query using “name” or “value”.

["and",
  ["=", "name", "operatingsystem"],
  ["=", "value", "Debian"]]

This will find all the “operatingsystem = Debian” facts, and their corresponding nodes. As you see, “and” is supported for facts, as are “or” and “not”.

Fact operators

As with resources, facts also support the ~ regular expression match operator, for all their fields. In addition to that, numeric comparisons are supported for fact values:

["and",
  ["=", "name", "uptime_seconds"],
  [">=", "value", 100000],
  ["<", "value", 1000000]]

This will find nodes for which the uptime_seconds fact is in the half-open range [100000, 1000000). Numeric comparisons will always be false for fact values which are not numeric. Importantly, version numbers such as 2.6.12 are not numeric, and the numeric comparison operators can’t be used with them at this time.

Nodes Walkthrough

We can also query for nodes. Once again, this is quite similar to resource and fact queries:

["=", "name", "foo.example.com"]

The result of this query is:

["foo.example.com"]

This will find the node foo.example.com. Note that the results of a node query contain only the node names, rather than an object with multiple fields as with resources and facts.

Querying on facts

Nodes can also be queried based on their facts, using the same operators as for fact queries:

["and",
  ["=", ["fact", "operatingsystem"], "Debian"],
  ["<", ["fact", "uptime_seconds"], 10000]]

This will return Debian nodes with uptime_seconds < 10000.

Subquery Walkthrough

The queries we’ve looked at so far are quite powerful and useful, but what if your query needs to consider both resources and facts? For instance, suppose you need the IP address of your Apache servers, to configure a load balancer. You could find those servers using this resource query:

["and",
  ["=", "type", "Class"],
  ["=", "title", "Apache"]]

This will find all the Class[Apache] resources, which each knows the certname of the node it came from. Then you could put all those certnames into a fact query:

["and",
  ["=", "name", "ipaddress"],
  ["or",
    ["=", "certname", "a.example.com"],
    ["=", "certname", "b.example.com"],
    ["=", "certname", "c.example.com"],
    ["=", "certname", "d.example.com"],
    ["=", "certname", "e.example.com"]]]

But this query is lengthy, and it requires some logic to assemble and run the second query. No, there has to be a better way. What if we could find the Class[Apache] servers and use the results of that directly to find the certname? It turns out we can, with this fact query:

["and",
  ["=", "name", "ipaddress"],
  ["in", "certname",
    ["extract", "certname", ["select-resources",
                              ["and",
                                ["=", "type", "Class"],
                                ["=", "title", "Apache"]]]]

This may appear a little daunting, so we’ll look at it piecewise.

Let’s start with “select-resources”. This operator takes one argument, which is a resource query, and returns the results of that query, in exactly the form you would expect to see them if you did a plain resource query.

We then use an operator called “extract” to turn our list of resources into just a list of certnames. So we now conceptually have something like

["in", "certname", ["foo.example.com", "bar.example.com", "baz.example.com"]]

The “in” operator matches facts whose “certname” is in the supplied list. (For now, that list has to be generated from a subquery, and can’t be supplied directly in the query, so if you want a literal list, you’ll unfortunately still have to use a combination of “or” and “=”). At this point, our query seems a lot like the one above, except we didn’t have to specify exactly which certnames to use, and instead we get them in the same query.

Similarly, there is a “select-facts” operator which will perform a fact subquery. Either kind of subquery is usable from every kind of query (facts, resources, and nodes), subqueries may be nested, and multiple subqueries may be used in a single query. Finding use cases for some of those combinations is left as an exercise to the reader.

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Docs: PuppetDB 1.1 » API » Query Tutorial