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TagIt

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TagIt is a tool that updates Consul service registration tags with outputs of a script. It copies the current service registration and appends the output of the script line by line as tags, while keeping the original tags.

Table of Contents

Why TagIt?

TagIt addresses a feature that's currently missing from Consul. You can read more about the need for this functionality in this Consul issue.

Here are some scenarios where TagIt can be useful:

  1. Database Leader Tagging: Ensure all writes go to the leader by tagging it appropriately.
  2. Non-Consul-Aware Service Discovery: Use Consul for service discovery with services that aren't Consul-aware.
  3. Web Server VHost Tagging: Tag all vhosts served by a web server or load balancer.
  4. Generic Service Tagging: Tag any services for Consul-based service discovery.

Installation

To install TagIt, use the following commands:

$ git clone https://github.com/ncode/tagit
$ cd tagit
$ go build

Usage

TagIt provides three main commands: run, cleanup, and systemd.

Run Command

The run command starts TagIt and continuously updates the tags based on the script output:

$ ./tagit run --consul-addr=127.0.0.1:8500 --service-id=my-service1 --script=./examples/tagit/example.sh --interval=5s --tag-prefix=tagit

Cleanup Command

The cleanup command removes all tags with the specified prefix from the service:

$ ./tagit cleanup --consul-addr=127.0.0.1:8500 --service-id=my-service1 --tag-prefix=tagit

Systemd Command

The systemd command generates a systemd service file for TagIt:

./tagit systemd --service-id=my-service1 --script=./examples/tagit/example.sh --tag-prefix=tagit --interval=5s --user=tagit --group=tagit

This command will output a systemd service file that you can use to run TagIt as a system service.

How It Works

TagIt interacts with Consul as follows:

sequenceDiagram
    participant tagit
    participant consul
    loop execute script on interval
        tagit->>consul: Query service with ID
        consul->>tagit: Return current service registration
        tagit->>tagit: Execute script and process output
        tagit->>consul: Update service registration with new tags
    end
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Examples

Here's an example of how to test TagIt:

  1. Start a Consul agent in development mode:

    consul agent -dev &

  2. Register a service with Consul:

    curl --request PUT --data @examples/consul/my-service1.json http://127.0.0.1:8500/v1/agent/service/register

  3. Run TagIt:

    ./tagit run --consul-addr=127.0.0.1:8500 --service-id=my-service1 --script=./examples/tagit/example.sh --interval=5s --tag-prefix=tagit

  4. Generate a systemd service file:

    ./tagit systemd --service-id=my-service1 --script=./examples/tagit/example.sh --tag-prefix=tagit --interval=5s --user=tagit --group=tagit > /etc/systemd/system/tagit-my-service1.service

  5. Clean up the tags:

    ./tagit cleanup --consul-addr=127.0.0.1:8500 --service-id=my-service1 --tag-prefix=tagit

Contributing

Contributions to TagIt are welcome! Please feel free to submit a Pull Request.

License

TagIt is licensed under the Apache License, Version 2.0. See the LICENSE file for details.