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---
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layout: "docs"
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page_title: "Prepared Queries (HTTP)"
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sidebar_current: "docs-agent-http-query"
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description: >
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The Query endpoints are used to manage and execute prepared queries.
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---
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# Prepared Query HTTP Endpoint
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The Prepared Query endpoints are used to create, update, destroy, and execute
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prepared queries.
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Prepared queries allow you to register a complex service query and then execute
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it later via its ID or name to get a set of healthy nodes that provide a given
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service. This is particularly useful in combination with Consul's
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[DNS Interface](/docs/agent/dns.html) as it allows for much richer queries than
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would be possible given the limited interface DNS provides.
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The following endpoints are supported:
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* [`/v1/query`](#general): Creates a new prepared query or lists
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all prepared queries
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* [`/v1/query/<query>`](#specific): Updates, fetches, or deletes
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a prepared query
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* [`/v1/query/<query or name>/execute`](#execute): Executes a
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prepared query by its ID or optional name
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Not all endpoints support blocking queries and all consistency modes,
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see details in the sections below.
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The query endpoints support the use of ACL tokens. Prepared queries have some
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special handling of ACL tokens that are highlighted in the sections below.
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### <a name="general"></a> /v1/query
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The general query endpoint supports the `POST` and `GET` methods.
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#### POST Method
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When using the `POST` method, Consul will create a new prepared query and return
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its ID if it is created successfully.
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By default, the datacenter of the agent is queried; however, the dc can be
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provided using the "?dc=" query parameter.
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The create operation expects a JSON request body that defines the prepared query,
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like this example:
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```javascript
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{
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"Name": "my-query",
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"Session": "adf4238a-882b-9ddc-4a9d-5b6758e4159e",
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"Service": {
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"Service": "redis",
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"Failover": {
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"NearestN": 3,
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"Datacenters": ["dc1", "dc2"]
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},
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"OnlyPassing": false,
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"Tags": ["master", "!experimental"]
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},
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"DNS": {
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"TTL": "10s"
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}
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}
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```
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Only the `Service` field inside the `Service` structure is mandatory, all other
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fields will take their default values if they are not included.
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`Name` is an optional friendly name that can be used to execute a query instead
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of using its ID.
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`Session` provides a way to automatically remove a prepared query when the
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given session is invalidated. This is optional, and if not given the prepared
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query must be manually removed when no longer needed.
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The set of fields inside the `Service` structure define the query's behavior.
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`Service` is the name of the service to query. This is required.
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`Failover` contains two fields, both of which are optional, and determine what
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happens if no healthy nodes are available in the local datacenter when the query
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is executed. It allows the use of nodes in other datacenters with very little
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configuration.
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If `NearestN` is set to a value greater than zero, then the query
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will be forwarded to up to `NearestN` other datacenters based on their estimated
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network round trip time using [Network Coordinates](/docs/internals/coordinates.html)
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from the WAN gossip pool. The median round trip time from the server handling the
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query to the servers in the remote datacenter is used to determine the priority.
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The default value is zero. All Consul servers must be running version 0.6.0 or
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above in order for this feature to work correctly. If any servers are not running
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the required version of Consul they will be considered last since they won't have
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any available network coordinate information.
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`Datacenters` contains a fixed list of remote datacenters to forward the query
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to if there are no healthy nodes in the local datacenter. Datacenters are queried
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in the order given in the list. If this option is combined with `NearestN`, then
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the `NearestN` queries will be performed first, followed by the list given by
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`Datacenters`. A given datacenter will only be queried one time during a failover,
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even if it is selected by both `NearestN` and is listed in `Datacenters`. The
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default value is an empty list.
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`OnlyPassing` controls the behavior of the query's health check filtering. If
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this is set to false, the results will include nodes with checks in the passing
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as well as the warning states. If this is set to true, only nodes with checks
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in the passing state will be returned. The default value is false.
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`Tags` provides a list of service tags to filter the query results. For a service
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to pass the tag filter it must have *all* of the required tags, and *none* of the
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excluded tags (prefixed with `!`). The default value is an empty list, which does
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no tag filtering.
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`TTL` in the `DNS` structure is a duration string that can use "s" as a
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suffix for seconds. It controls how the TTL is set when query results are served
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over DNS. If this isn't specified, then the Consul agent configuration for the given
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service will be used (see [DNS Caching](/docs/guides/dns-cache.html)). If this is
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specified, it will take precedence over any Consul agent-specific configuration.
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If no TTL is specified here or at the Consul agent level, then the TTL will
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default to 0.
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The return code is 200 on success and the ID of the created query is returned in
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a JSON body:
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```javascript
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{
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"ID": "8f246b77-f3e1-ff88-5b48-8ec93abf3e05"
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}
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```
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If ACLs are enabled, then the provided token will be used to check access to
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the service being queried, and it will be saved along with the query for use
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when the query is executed. This is key to allowing prepared queries to work
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via the DNS interface, and it's important to note that prepared query IDs and
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names become a read-only proxy for the token used to create the query.
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The query IDs that Consul generates are done in the same manner as ACL tokens,
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so provide equal strength, but names may be more guessable and should be used
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carefully with ACLs. Also, the token used to create the prepared query (or a
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management token) is required to read the query back, so the ability to execute
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a prepared query is not enough to get access to the actual token.
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#### GET Method
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When using the GET method, Consul will provide a listing of all prepared queries.
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By default, the datacenter of the agent is queried; however, the dc can be
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provided using the "?dc=" query parameter. This endpoint supports blocking
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queries and all consistency modes.
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Since this listing includes sensitive ACL tokens, this is a privileged endpoint
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and always requires a management token to be supplied if ACLs are enabled.
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This returns a JSON list of prepared queries, which looks like:
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```javascript
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[
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{
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"ID": "8f246b77-f3e1-ff88-5b48-8ec93abf3e05",
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"Name": "my-query",
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"Session": "adf4238a-882b-9ddc-4a9d-5b6758e4159e",
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"Token": "",
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"Service": {
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"Service": "redis",
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"Failover": {
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"NearestN": 3,
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"Datacenters": ["dc1", "dc2"]
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},
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"OnlyPassing": false,
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"Tags": ["master", "!experimental"]
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},
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"DNS": {
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"TTL": "10s"
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},
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"RaftIndex": {
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"CreateIndex": 23,
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"ModifyIndex": 42
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}
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}
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]
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```
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### <a name="specific"></a> /v1/query/\<query\>
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The query-specific endpoint supports the `GET`, `PUT`, and `DELETE` methods. The
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\<query\> argument is the ID of an existing prepared query.
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#### PUT Method
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The `PUT` method allows an existing prepared query to be updated.
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By default, the datacenter of the agent is queried; however, the dc can be
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provided using the "?dc=" query parameter.
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If ACLs are enabled, then the same token used to create the query (or a
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management token) must be supplied.
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The body is the same as is used to create a prepared query, as described above.
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If the API call succeeds, a 200 status code is returned.
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#### GET Method
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The `GET` method allows an existing prepared query to be fetched.
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By default, the datacenter of the agent is queried; however, the dc can be
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provided using the "?dc=" query parameter. This endpoint supports blocking
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queries and all consistency modes.
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The returned response is the same as the list of prepared queries above,
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only with a single item present. If the query does not exist then a 404
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status code will be returned.
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If ACLs are enabled, then the same token used to create the query (or a
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management token) must be supplied.
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#### DELETE Method
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The `DELETE` method is used to delete a prepared query.
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By default, the datacenter of the agent is queried; however, the dc can be
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provided using the "?dc=" query parameter.
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If ACLs are enabled, then the same token used to create the query (or a
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management token) must be supplied.
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No body is required as part of this request.
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If the API call succeeds, a 200 status code is returned.
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### <a name="execute"></a> /v1/query/\<query or name\>/execute
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The query execute endpoint supports only the `GET` method and is used to
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execute a prepared query. The \<query or name\> argument is the ID or name
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of an existing prepared query.
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By default, the datacenter of the agent is queried; however, the dc can be
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provided using the "?dc=" query parameter. This endpoint does not support
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blocking queries, but it does support all consistency modes.
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Adding the optional "?near=" parameter with a node name will sort the resulting
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list in ascending order based on the estimated round trip time from that node.
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Passing "?near=_agent" will use the agent's node for the sort. If this is not
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present, then the nodes will be shuffled randomly and will be in a different
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order each time the query is executed.
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An optional "?limit=" parameter can be used to limit the size of the list to
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the given number of nodes. This is applied after any sorting or shuffling.
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The ACL token supplied when the prepared query was created will be used to
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execute the request, so no ACL token needs to be supplied (it will be ignored).
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No body is required as part of this request.
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If the query does not exist then a 404 status code will be returned. Otherwise,
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a JSON body will be returned like this:
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```javascript
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{
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"Service": "redis",
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"Nodes": [
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{
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"Node": {
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"Node": "foobar",
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"Address": "10.1.10.12"
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},
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"Service": {
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"ID": "redis",
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"Service": "redis",
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"Tags": null,
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"Port": 8000
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},
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"Checks": [
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{
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"Node": "foobar",
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"CheckID": "service:redis",
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"Name": "Service 'redis' check",
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"Status": "passing",
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"Notes": "",
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"Output": "",
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"ServiceID": "redis",
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"ServiceName": "redis"
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},
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{
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"Node": "foobar",
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"CheckID": "serfHealth",
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"Name": "Serf Health Status",
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"Status": "passing",
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"Notes": "",
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"Output": "",
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"ServiceID": "",
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"ServiceName": ""
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}
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],
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"DNS": {
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"TTL": "10s"
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},
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"Datacenter": "dc3",
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"Failovers": 2
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}
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}
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```
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The `Nodes` section contains the list of healthy nodes providing the given
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service, as specified by the constraints of the prepared query.
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`Service` has the service name that the query was selecting. This is useful
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for context in case an empty list of nodes is returned.
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`DNS` has information used when serving the results over DNS. This is just a
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copy of the structure given when the prepared query was created.
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`Datacenter` has the datacenter that ultimately provided the list of nodes
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and `Failvovers` has the number of remote datacenters that were queried
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while executing the query. This provides some insight into where the data
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came from. This will be zero during non-failover operations where there
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were healthy nodes found in the local datacenter.
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James Phillips