## Receptor Mesh AWX uses a [Receptor](https://github.com/ansible/receptor) mesh to transmit "user-space" unified jobs: - jobs - ad hoc commands - inventory updates to the node where they run. > NOTE: user-space jobs are what carry out the user's Ansible automation. These job types run inside of the designated execution environment so that the needed content is available. > NOTE: The word "node" corresponds to entries in the `Instance` database model, or the `/api/v2/instances/` endpoint, and is a machine participating in the cluster / mesh. The unified jobs API reports `controller_node` and `execution_node` fields. The execution node is where the job runs, and the controller node interfaces between the job and server functions. Before a job can start, the controller node prepares the `private_data_dir` needed for the job to run. Next, the controller node sends the data via `ansible-runner`'s `transmit`, and connects to the output stream with `process`. For details on these commands, see the [ansible-runner docs on remote execution](https://ansible-runner.readthedocs.io/en/latest/remote_jobs.html). On the other side, the execution node runs the job under `ansible-runner worker`. ### Split of Control Plane versus Execution Plane Instances in the **control plane** run persistent AWX services (like the web server, task dispatcher, etc.), project updates, and management jobs. The task manager logic will not send user-space jobs to **control-only** nodes. In the inventory definition, the user can set a flag to designate this node type. **Execution-only** nodes have a minimal set of software requirements needed to participate in the receptor mesh and run jobs under ansible-runner with podman isolation. These _only_ run user-space jobs, and may be geographically separated (with high latency) from the control plane. They may not even have a direct connection to the cluster, and use other receptor **hop** nodes to communicate. The hop and execution-only nodes may be referred to collectively as the **execution plane**. **Hybrid** (control & execution nodes) are instances in the control plane that are allowed to run user-space jobs. #### Receptor Configuration Work Type Execution-only nodes need to advertise the "ansible-runner" work type. User-space jobs are submitted as a receptor work unit with this work type. An entry like this should appear in its `receptor.conf` (receptor configuration file): ``` - work-command: worktype: ansible-runner command: ansible-runner params: worker allowruntimeparams: true ``` Control (and hybrid) nodes advertise the "local" work type instead. So the entry is the same as above, except that it has `worktype: local`. Project updates are submitted as this work type. If user-space jobs run on a hybrid node, they will also run as the "local" work type. Here is a listing of work types that you may encounter: - `local` - any ansible-runner job ran in a traditional install - `ansible-runner` - remote execution of user-space jobs - `kubernetes-runtime-auth` - user-space jobs ran in a container group - `kubernetes-incluster-auth` - project updates and management jobs on OpenShift Container Platform ### Auto-discovery of execution nodes Instances in control plane must be registered by the installer via `awx-manage` commands like `awx-manage register_queue` or `awx-manage register_instance`. Execution-only nodes are automatically discovered after they have been configured and join the receptor mesh. Control nodes should see them as a "Known Node". Control nodes check the receptor network (reported via `receptorctl status`) when their heartbeat task runs. Nodes on the receptor network are compared against the `Instance` model in the database. If a node appears in the mesh network which is not in the database, then a "health check" is started. The `capacity` field will obtain a non-zero value through this process, which is necessary to run jobs. #### Health Check Mechanics All relevant data for health checks is reported from the ansible-runner command: ``` ansible-runner worker --worker-info ``` This will output YAML data to standard out containing CPU, memory, and other metrics used to compute `capacity`. AWX invokes this command by submitting a receptor work unit (of type `ansible-runner`) to the target execution node. If you have the development environment running, you can run a one-off health check of a node with this command: ``` echo "from awx.main.utils.receptor import worker_info; worker_info('receptor-1')" | awx-manage shell_plus --quiet ``` This must be ran as the awx user inside one of the hybrid or control nodes. This will not affect actual `Instance` record, but will just run the command and report the data. ### Development Environment A cluster (of containers) with execution nodes and a hop node is created by the docker-compose Makefile target. By default, it will create 1 hybrid node, 1 hop node, and 2 execution nodes. You can switch the type of AWX nodes between hybrid and control with this syntax. ``` MAIN_NODE_TYPE=control COMPOSE_TAG=devel make docker-compose ``` Running the above command will create a cluster of 1 control node, 1 hop node, and 2 execution nodes. The number of nodes can be changed: ``` CONTROL_PLANE_NODE_COUNT=2 EXECUTION_NODE_COUNT=3 COMPOSE_TAG=devel make docker-compose ``` This will spin up a topology represented below. (names are the receptor node names, which differ from the AWX Instance names and network address in some cases) ``` ┌──────────────┐ │ │ ┌──────────────┐ ┌──────────┤ receptor-1 │ │ │ │ │ │ │ awx_1 │◄──────────┐ │ └──────────────┘ │ │ │ ▼ └──────┬───────┘ ┌──────┴───────┐ ┌──────────────┐ │ │ │ │ │ │ │ receptor-hop │◄───────┤ receptor-2 │ ▼ │ │ │ │ ┌──────────────┐ └──────────────┘ └──────────────┘ │ │ ▲ │ awx_2 │ │ ┌──────────────┐ │ │ │ │ │ └──────────────┘ └──────────┤ receptor-3 │ │ │ └──────────────┘ ``` All execution (`receptor-*`) nodes connect to the hop node. Only the `awx_1` node connects to the hop node out of the AWX cluster. `awx_1` connects to `awx_2`, fulfilling the requirement that the AWX cluster is fully connected. For an example, if a job is launched with `awx_2` as the `controller_node` and `receptor-3` as the `execution_node`, then `awx_2` communicates to `receptor-3` via `awx_1` and then `receptor-hop`.