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95 lines
5.5 KiB
Markdown
95 lines
5.5 KiB
Markdown
# Design
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In the design described below, our "private cloud" platform is:
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* **Highly-available** (_can tolerate the failure of a single component_)
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* **Scalable** (_can add resource or capacity as required_)
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* **Portable** (_run it on your garage server today, run it in AWS tomorrow_)
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* **Secure** (_access protected with [LetsEncrypt certificates](/ha-docker-swarm/traefik/) and optional [OIDC with 2FA](/ha-docker-swarm/traefik-forward-auth/)_)
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* **Automated** (_requires minimal care and feeding_)
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## Design Decisions
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**Where possible, services will be highly available.**
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This means that:
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* At least 3 docker swarm manager nodes are required, to provide fault-tolerance of a single failure.
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* [Ceph](/ha-docker-swarm/shared-storage-ceph/) is employed for share storage, because it too can be made tolerant of a single failure.
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!!! note
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An exception to the 3-nodes decision is running a single-node configuration. If you only **have** one node, then obviously your swarm is only as resilient as that node. It's still a perfectly valid swarm configuration, ideal for starting your self-hosting journey. In fact, under the single-node configuration, you don't need ceph either, and you can simply use the local volume on your host for storage. You'll be able to migrate to ceph/more nodes if/when you expand.
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**Where multiple solutions to a requirement exist, preference will be given to the most portable solution.**
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This means that:
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* Services are defined using docker-compose v3 YAML syntax
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* Services are portable, meaning a particular stack could be shut down and moved to a new provider with minimal effort.
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## Security
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Under this design, the only inbound connections we're permitting to our docker swarm in a **minimal** configuration (*you may add custom services later, like UniFi Controller*) are:
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### Network Flows
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* **HTTP (TCP 80)** : Redirects to https
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* **HTTPS (TCP 443)** : Serves individual docker containers via SSL-encrypted reverse proxy
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### Authentication
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* Where the hosted application provides a trusted level of authentication (*i.e., [NextCloud](/recipes/nextcloud/)*), or where the application requires public exposure (*i.e. [Privatebin](/recipes/privatebin/)*), no additional layer of authentication will be required.
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* Where the hosted application provides inadequate (*i.e. [NZBGet](/recipes/autopirate/nzbget/)*) or no authentication (*i.e. [Gollum](/recipes/gollum/)*), a further authentication against an OAuth provider will be required.
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## High availability
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### Normal function
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Assuming a 3-node configuration, under normal circumstances the following is illustrated:
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* All 3 nodes provide shared storage via Ceph, which is provided by a docker container on each node.
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* All 3 nodes participate in the Docker Swarm as managers.
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* The various containers belonging to the application "stacks" deployed within Docker Swarm are automatically distributed amongst the swarm nodes.
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* Persistent storage for the containers is provide via cephfs mount.
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* The **traefik** service (*in swarm mode*) receives incoming requests (*on HTTP and HTTPS*), and forwards them to individual containers. Traefik knows the containers names because it's able to read the docker socket.
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* All 3 nodes run keepalived, at varying priorities. Since traefik is running as a swarm service and listening on TCP 80/443, requests made to the keepalived VIP and arriving at **any** of the swarm nodes will be forwarded to the traefik container (*no matter which node it's on*), and then onto the target backend.
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### Node failure
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In the case of a failure (or scheduled maintenance) of one of the nodes, the following is illustrated:
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* The failed node no longer participates in Ceph, but the remaining nodes provide enough fault-tolerance for the cluster to operate.
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* The remaining two nodes in Docker Swarm achieve a quorum and agree that the failed node is to be removed.
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* The (*possibly new*) leader manager node reschedules the containers known to be running on the failed node, onto other nodes.
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* The **traefik** service is either restarted or unaffected, and as the backend containers stop/start and change IP, traefik is aware and updates accordingly.
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* The keepalived VIP continues to function on the remaining nodes, and docker swarm continues to forward any traffic received on TCP 80/443 to the appropriate node.
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### Node restore
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When the failed (*or upgraded*) host is restored to service, the following is illustrated:
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* Ceph regains full redundancy
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* Docker Swarm managers become aware of the recovered node, and will use it for scheduling **new** containers
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* Existing containers which were migrated off the node are not migrated backend
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* Keepalived VIP regains full redundancy
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### Total cluster failure
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A day after writing this, my environment suffered a fault whereby all 3 VMs were unexpectedly and simultaneously powered off.
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Upon restore, docker failed to start on one of the VMs due to local disk space issue[^1]. However, the other two VMs started, established the swarm, mounted their shared storage, and started up all the containers (services) which were managed by the swarm.
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In summary, although I suffered an **unplanned power outage to all of my infrastructure**, followed by a **failure of a third of my hosts**... ==all my platforms are 100% available with **absolutely no manual intervention**==.
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[^1]: Since there's no impact to availability, I can fix (or just reinstall) the failed node whenever convenient.
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## Chef's Notes 📓 |