70 lines
2.9 KiB
Markdown
70 lines
2.9 KiB
Markdown
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# `mempool`
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Deploys the [Mempool](https://mempool.space) block explorer as a three-container
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Docker Compose stack — MariaDB, backend, frontend — on `mempool-box`, and keeps a
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health check on each.
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Converted from `deploy_mempool_playbook.yml` (745 lines) under Plan 6. The
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playbook is now 37 lines: this role, plus a second play that publishes the
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frontend through Caddy on the edge host.
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## Phases
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| `docker.yml` | Docker engine: repo, key, packages, service |
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| `deploy.yml` | directories, `docker-compose.yml`, pull, up, wait-for-healthy |
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| `healthcheck.yml` | three check scripts, three services, three timers |
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## Three health checks, not one
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Mempool is three moving parts and knowing *which* one is down is the point, so
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each gets its own check, unit and timer, driven by the `mempool_healthchecks`
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list:
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| | checks |
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| `mariadb` | `docker inspect` health status of `mempool-db` |
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| `backend` | `GET /api/v1/backend-info` |
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| `frontend` | `GET /` |
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Each records its answer in its exit code, which systemd keeps:
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`systemctl is-failed mempool-backend-healthcheck.service`. Reporting elsewhere
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is one field per check, `push_url`, and is the plug-in point for whatever
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monitoring exists. Empty means check, exit honestly, report nowhere. The URLs
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are credentials, so callers pass them from the vault.
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Nothing here is specific to a monitoring product. The embedded Python that
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created monitors over the Uptime Kuma API, the `/tmp` credentials file, the
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push-URL file read back and parsed, and three systemd `Environment=` rewrites
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are gone.
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## MariaDB owns its own data directory
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`{{ mempool_mysql_dir }}` is bind-mounted into the container, which runs as uid
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**999** and must create files there. The playbook this replaced declared
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`owner: "{{ ansible_user }}"` (1000) on it, which had drifted from reality ever
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since the containers were created — unnoticed, because the playbook had not been
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run since.
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That was not academic. The first real run of this role pulled a newer
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`mariadb:10.11` and recreated `mempool-db`; had the chown still been in place,
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MariaDB would have come back to a directory it could not write. The role now
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ensures the directory exists and leaves ownership to the container.
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## `mempool_frontend_port` lives in `services_config.yml`
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Two hosts need it: this role deploys the frontend on `mempool-box`, and the Caddy
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play proxies to it from the edge host. A role default is invisible to the second
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play, so the value lives in `service_settings.mempool.frontend_port` and the role
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default derives from it.
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## Expect `changed=2` on a converged host
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`Pull Mempool images` and `Deploy Mempool containers with docker compose` are
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bare `command:` tasks with no `changed_when`, so they always report changed.
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That is the idempotent floor, not drift. Everything else reports `ok`.
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**`mariadb:10.11` is a moving tag**, so a run can pull a newer patch release and
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recreate the database container. Pin it if that is not what you want.
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