Target nodes spec

Target nodes spec

Default is for all nodes to execute each job. Dkron has the ability to run jobs in specific nodes by leveraging the use of tags. You can choose whether a job is run on a node or group of nodes by specifying tags and a count of target nodes having this tag do you want a job to run.

The target node syntax is:

"tag": "value[:count]"

To achieve this Nodes and Jobs have tags, for example, having a node with the following tags:

{
    "tags": {
        "dc": "dc1",
        "expect": "3",
        "port": "6868",
        "region": "global",
        "role": "dkron",
        "rpc_addr": "10.88.94.129:6868",
        "server": "true",
        "version": "devel",
        "my_role": "web"
    }
}

tip

You can specify tags for nodes in the dkron config file or in the command line using --tags parameter

In case there is no matching nodes with the specified tags, the job will not run.

Following some examples using different tag combinations:

Target all nodes with a tag

{
    "name": "job_name",
    "command": "/bin/true",
    "schedule": "@every 2m",
    "tags": {
        "my_role": "web"
    }
}

Target only one nodes of a group of nodes with a tag

{
    "name": "job_name",
    "command": "/bin/true",
    "schedule": "@every 2m",
    "tags": {
        "my_role": "web:1"
    }
}

Dkron will try to run the job in the amount of nodes indicated by that count having that tag.

Details and limitations

• Tags specified in a Job are combined using AND, therefore a job that specifies several tags like:

{
    "tags": {
        "my_role": "web",
        "role": "dkron"
    }
}

Will try to run the job in nodes that have all speciefied tags.

There is no limit in the tags that a job can have but having a Job with several tags with count like:

{
    "tags": {
        "my_role": "web:1",
        "role": "dkron:2"
    }
}

Will try to run the job in nodes that have all specified tags and using the lowest count. In the last example, it will run in one node having "my_role": "web" and "role": "dkron" tag, even if there is more than one node with these tags.