diff --git a/prepare-vms/lib/commands.sh b/prepare-vms/lib/commands.sh
index e409f2f4..f668ced0 100644
--- a/prepare-vms/lib/commands.sh
+++ b/prepare-vms/lib/commands.sh
@@ -498,12 +498,12 @@ _cmd_helmprom() {
     if i_am_first_node; then
         kubectl -n kube-system get serviceaccount helm ||
             kubectl -n kube-system create serviceaccount helm
-        helm init --service-account helm
+        sudo -u docker -H helm init --service-account helm
         kubectl get clusterrolebinding helm-can-do-everything ||
             kubectl create clusterrolebinding helm-can-do-everything \
                 --clusterrole=cluster-admin \
                 --serviceaccount=kube-system:helm
-        helm upgrade --install prometheus stable/prometheus \
+        sudo -u docker -H helm upgrade --install prometheus stable/prometheus \
             --namespace kube-system \
             --set server.service.type=NodePort \
             --set server.service.nodePort=30090 \
diff --git a/slides/k8s/prometheus.md b/slides/k8s/prometheus.md
index b6777a6c..f0cb2a92 100644
--- a/slides/k8s/prometheus.md
+++ b/slides/k8s/prometheus.md
@@ -12,7 +12,7 @@
 
   - an *alert manager* to notify us according to metrics values or trends
 
-- We are going to deploy it on our Kubernetes cluster and see how to query it
+- We are going to use it to collect and query some metrics on our Kubernetes cluster
 
 ---
 
@@ -145,7 +145,28 @@ scrape_configs:
 
   (it will even be gentler on the I/O subsystem since it needs to write less)
 
-[Storage in Prometheus 2.0](https://www.youtube.com/watch?v=C4YV-9CrawA) by [Goutham V](https://twitter.com/putadent) at DC17EU
+- Would you like to know more? Check this video:
+
+  [Storage in Prometheus 2.0](https://www.youtube.com/watch?v=C4YV-9CrawA) by [Goutham V](https://twitter.com/putadent) at DC17EU
+
+---
+
+## Checking if Prometheus is installed
+
+- Before trying to install Prometheus, let's check if it's already there
+
+.exercise[
+
+- Look for services with a label `app=prometheus` across all namespaces:
+  ```bash
+  kubectl get services --selector=app=prometheus --all-namespaces
+  ```
+
+]
+
+If we see a `NodePort` service called `prometheus-server`, we're good!
+
+(We can then skip to "Connecting to the Prometheus web UI".)
 
 ---
 
@@ -210,20 +231,41 @@ We need to:
 
 - Install Prometheus on our cluster:
   ```bash
-  helm install stable/prometheus \
-         --set server.service.type=NodePort \
-         --set server.persistentVolume.enabled=false
+    helm upgrade prometheus stable/prometheus \
+        --install \
+        --namespace kube-system \
+        --set server.service.type=NodePort \
+        --set server.service.nodePort=30090 \
+        --set server.persistentVolume.enabled=false \
+        --set alertmanager.enabled=false
   ```
 
 ]
 
-The provided flags:
+Curious about all these flags? They're explained in the next slide.
 
-- expose the server web UI (and API) on a NodePort
+---
 
-- use an ephemeral volume for metrics storage
-  <br/>
-  (instead of requesting a Persistent Volume through a Persistent Volume Claim)
+class: extra-details
+
+## Explaining all the Helm flags
+
+- `helm upgrade prometheus` → upgrade release "prometheus" to the latest version ...
+
+  (a "release" is a unique name given to an app deployed with Helm)
+
+- `stable/prometheus` → ... of the Chart `prometheus` in repo `stable`
+
+- `--install` → if the app doesn't exist, create it
+
+- `--namespace kube-system` → put it in that specific namespace
+
+- And set the following *values* when rendering the Chart's templates:
+
+  - `server.service.type=NodePort` → expose the Prometheus server with a NodePort
+  - `server.service.nodePort=30090` → set the specific NodePort number to use
+  - `server.persistentVolume.enabled=false` → do not use a PersistentVolumeClaim
+  - `alertmanager.enabled=false` → disable the alert manager entirely
 
 ---
 
@@ -235,7 +277,7 @@ The provided flags:
 
 - Figure out the NodePort that was allocated to the Prometheus server:
   ```bash
-  kubectl get svc | grep prometheus-server
+  kubectl get svc --all-namespaces | grep prometheus-server
   ```
 
 - With your browser, connect to that port
@@ -292,7 +334,7 @@ This query will show us CPU usage across all containers:
 container_cpu_usage_seconds_total
 ```
 
-- The suffix of the metrics name tells us: 
+- The suffix of the metrics name tells us:
 
   - the unit (seconds of CPU)
 
@@ -486,3 +528,21 @@ class: extra-details
   - see [this comment](https://github.com/prometheus/prometheus/issues/2204#issuecomment-261515520) for an overview
 
   - or [this blog post](https://5pi.de/2017/11/09/use-prometheus-vector-matching-to-get-kubernetes-utilization-across-any-pod-label/) for a complete description of the process
+
+---
+
+## In practice
+
+- Grafana is a beautiful (and useful) frontend to display all kinds of graphs
+
+- Not everyone needs to know Prometheus, PromQL, Grafana, etc.
+
+- But in a team, it is valuable to have at least one person who know them
+
+- That person can set up queries and dashboards for the rest of the team
+
+- It's a little bit likeknowing how to optimize SQL queries, Dockerfiles ...
+
+  Don't panic if you don't know these tools!
+
+  ... But make sure at least one person in your team is on it 💯