OpenSearch/watcher/docs/reference/input/chain.asciidoc

[[input-chain]]
==== Chain Input

An <<input, input>> that enables you to string together multiple inputs to load data into the watch execution
context. Each input loads data into the execution context and that data is available to subsequent inputs in the chain.

The `chain` input is useful when you want to perform an action based on data from multiple sources. 
You can also use the data collected by one input to load data from another source. 

To reference data loaded by a particular input, you use the input's name, `ctx.payload.<input-name>.<value>`.

For example, the following chain input loads data from an HTTP server using the path set by a `simple` input.

[source,json]
--------------------------------------------------
{
  "input" : {
    "chain" : {
      "inputs" : [ <1>
        {
          "first" : {
            "simple" : { "path" : "/_search" }
          }
        },
        {
          "second" : {
            "http" : {
              "request" : {
                "host" : "localhost",
                "port" : 9200,
                "path" : "{{ctx.payload.first.path}}" <2>
              }
            }
          }
        }
      ]
    }
  }
  ...
}
--------------------------------------------------
<1> The inputs in a chain are specified as an array to guarantee the order in which the inputs are processed. (JSON does not guarantee the order of arbitrary objects.)
<2> Loads the `path` set by the `first` input.