How to do join query in elasticsearch?

I am having a hard time in ES join query, I googled a lot but find nothing helpful. So I ask here.

1. Mappings

I have 2 index, whose mapping is:

mappings for index logs:

"logs": {
        "properties": {
            "timestamp": {"type": "date"},
            "host": {"type": "keyword"},
            "log": {"type": "text"}

}

mapping for index versions:

"versions": {
        "properties": {
            "host": {"type": "keyword"},
            "version": {"type": "keyword"}

}

2. Sample Data

Suppose I have data like this:

Data for logs:

timestamp:1, host:a1, log: "sample log1"
timestamp:2, host:a1, log: "sample log2"
timestamp:3, host:a1, log: "sample log3"
timestamp:1, host:a2, log: "sample log4"
timestamp:2, host:a2, log: "sample log5"
timestamp:3, host:a2, log: "sample log6"
timestamp:1, host:a3, log: "sample log7"
timestamp:2, host:a3, log: "sample log8"
timestamp:3, host:a3, log: "sample log9"

Data for versions:

host:a1, version:v1
host:a2, version:v1
host:a3, version:v2

3. Purpose & Expected Result

What I want to query is: "Find out all logs of host's version equal to v1"

The result should be:

timestamp:1, host:a1, log: "sample log1"
timestamp:2, host:a1, log: "sample log2"
timestamp:3, host:a1, log: "sample log3"
timestamp:1, host:a2, log: "sample log4"
timestamp:2, host:a2, log: "sample log5"
timestamp:3, host:a2, log: "sample log6"

How should I do it? Please help.

Solution

Elasticsearch is not a relational database, and therefore does not support join.

The only ways to workaround this, with many cons, is to either use parent-child (or join data type in v6) or nested docs.

** both options are not that scalable and may introduce performance issues.