docs(mpp): document MP+ specifics and firewall rules

docs/deployment/specifics/clusters.md

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+---
+title: Clusters
+---
+
+## Automotive → MP+
+
+Currently we are moving from the Automotive cluster to the MP+ cluster. Our
+staging deployment is already present on the MP+ and there were some differences
+introduced once the migration started.
+
+### Namespaces
+
+Previously we have used a rather simple `packit-{{ deployment }}` namespace. On
+MP+ we are given `packit` as a tenant prefix, that needs to be separated from
+our custom namespaces by `--`, therefore we use `packit--stg` and
+`packit--stg-sandbox`.
+
+### Postgres
+
+On MP+ we have also moved to the newer postgres image, specifically we have used
+v13 and moved on to the v15.
+
+### Logging
+
+On Automotive cluster we're using fluentd-sidecar to upload the logs to the
+Splunk. Within the MP+ cluster we don't need to, since the logs can be output to
+the `stdout` and are logged implicitly.
+
+### Firewall
+
+Outgoing connections on the MP+ are implicitly denied and firewall rules must be
+explicitly requested. `10.0.0.0/8` network access from within our sandbox is
+explicitly denied.
+
+#### Requesting firewall rules
+
+1. Search for “egress firewall rules OSD” on Source
+2. Shiny link _opening a ticket_
+3. You can take an inspiration from RITM1861658; almost all of our tickets for
+   firewall rules follow the template below.
+
+#### Template and notes
+
+```
+• source: ‹list the clusters here›
+• destination: ‹list of domains›
+• protocol: 80, 443
+• justification: ‹almost as our release notes›
+(N clusters × M domains × P ports)
+```
+
+If you want to include subdomains, I would recommend typing it as
+`.example.com`, e.g. `.kde.org`.
+
+Don't forget to replace the `N`, `M`, and `P` with their respective values, it
+is used just as a check. You can also link the original issue with the waiting
+list, not required though.
+
+If you need to request outgoing SSH to be allowed (e.g. SSH access to git
+forges), don't forget to specify port 22 (which is the usual default), **and**
+instead of domain, give **IP addresses**. SSH access is bound by IPs rather than
+domains (can be seen in the “inspiration” ticket mentioned above).