Additional details for rook migration

content/u/blog/2022-08-27-migrating-ceph-nautilus-into-kubernetes-with-rook/contents.lr

@@ -334,6 +334,131 @@ So today we start with
 Using BGP and calico, the kubernetes cluster is setup "as usual" (for
 ungleich terms).
 
+### Ceph.conf change
+
+Originally our ceph.conf contained:
+
+```
+public network  = 2a0a:e5c0:0:0::/64
+cluster network = 2a0a:e5c0:0:0::/64
+```
+
+As of today they are removed and all daemons are restarted, allowing
+the native cluster to speak with the kubernetes cluster.
+
+### Setting up rook
+
+Usually we deploy rook via argocd. However as we want to be easily
+able to do manual intervention, we will first bootstrap rook via helm
+directly and turn off various services
+
+```
+helm repo add rook https://charts.rook.io/release
+helm repo update
+```
+
+We will use rook 1.8, as it is the last version to support Ceph
+nautilus, which is our current ceph version. The latest 1.8 version is
+1.8.10 at the moment.
+
+```
+helm upgrade --install --namespace rook-ceph --create-namespace --version v1.8.10 rook-ceph rook/rook-ceph
+```
+
+### Joining the 2 clusters, step 1: monitors and managers
+
+In the first step we want to add rook based monitors and managers
+and replace the native ones. For rook to be able to talk to our
+existing cluster, it needs to know
+
+* the current monitors/managers ("the monmap")
+* the right keys to talk to the existing cluster
+* the fsid
+
+As we are using v1.8, we will follow
+[the guidelines for disaster recover of rook
+1.8](https://www.rook.io/docs/rook/v1.8/ceph-disaster-recovery.html).
+
+Later we will need to create all the configurations so that rook knows
+about the different pools.
+
+### Rook: CephCluster
+
+Rook has a configuration of type `CephCluster` that typically looks
+something like this:
+
+```
+apiVersion: ceph.rook.io/v1
+kind: CephCluster
+metadata:
+  name: rook-ceph
+  namespace: rook-ceph
+spec:
+  cephVersion:
+    # see the "Cluster Settings" section below for more details on which image of ceph to run
+    image: quay.io/ceph/ceph:{{ .Chart.AppVersion }}
+  dataDirHostPath: /var/lib/rook
+  mon:
+    count: 5
+    allowMultiplePerNode: false
+  storage:
+    useAllNodes: true
+    useAllDevices: true
+    onlyApplyOSDPlacement: false
+  mgr:
+    count: 1
+    modules:
+      - name: pg_autoscaler
+        enabled: true
+  network:
+    ipFamily: "IPv6"
+    dualStack: false
+  crashCollector:
+    disable: false
+    # Uncomment daysToRetain to prune ceph crash entries older than the
+    # specified number of days.
+    daysToRetain: 30
+```
+
+For migrating, we don't want rook in the first stage to create any
+OSDs. So we will replace `useAllNodes: true` with `useAllNodes: false`
+and `useAllDevices: true` also with `useAllDevices: false`.
+
+### Extracting a monmap
+
+To get access to the existing monmap, we can export it from the native
+cluster using `ceph-mon -i {mon-id} --extract-monmap {map-path}`.
+More details can be found on the [documentation for adding and
+removing ceph
+monitors](https://docs.ceph.com/en/latest/rados/operations/add-or-rm-mons/).
+
+
+
+### Rook and Ceph pools
+
+Rook uses `CephBlockPool` to describe ceph pools as follows:
+
+```
+apiVersion: ceph.rook.io/v1
+kind: CephBlockPool
+metadata:
+  name: hdd
+  namespace: rook-ceph
+spec:
+  failureDomain: host
+  replicated:
+    size: 3
+  deviceClass: hdd
+```
+
+In this particular cluster we have 2 pools:
+
+- one (ssd based, device class = ssd)
+- hdd (hdd based, device class = hdd-big)
+
+The device class "hdd-big" is specific to this cluster as it used to
+contain 2.5" and 3.5" HDDs in different pools.
+
 
 
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