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+---
+layout: post
+author: Sam Hadow
+tags: podman, mongodb, containers
+---
+
+On my server I self host Overleaf with containers (podman) and Overleaf requires MongoDB as a database. Each version of Overleaf has a minimum required version of MongoDB and therefore you might have to upgrade your MongoDB container at one point. I'll explain step by step how I did it in my case.  
+
+# Upgrade steps
+
+As stated in the official [documentation](https://docs.overleaf.com/on-premises/maintenance/updating-mongodb), MongoDB requires step by step upgrades.  
+The intermediary version when upgrading (starting from version 4.0) are:  
+4.0, 4.2, 4.4, 5.0, 6.0, 7.0, 8.0  
+
+In my case I had to upgrade from version 6.0 to version 8.0  
+
+I now have the following in my Mongodb systemd unit managing the container:
+
+```ini
+[Unit]
+Description=Podman container-overleaf-mongo.service
+Documentation=man:podman-generate-systemd(1)
+Wants=network-online.target
+After=network-online.target
+RequiresMountsFor=%t/containers
+BindsTo=pod-overleaf.service
+After=pod-overleaf.service
+
+[Service]
+Environment=PODMAN_SYSTEMD_UNIT=%n
+Restart=on-failure
+TimeoutStopSec=70
+ExecStart=/usr/bin/podman run \
+	--cidfile=%t/%n.ctr-id \
+	--cgroups=no-conmon \
+	--rm \
+	--pod-id-file %t/pod-overleaf.pod-id \
+	--sdnotify=conmon \
+	--replace \
+	-d \
+	-e MONGO_INITDB_DATABASE=sharelatex \
+	-v /home/data/podman/overleaf/mongo_data:/data/db:Z \
+	-v /home/data/podman/overleaf/initdb.js:/docker-entrypoint-initdb.d/mongodb-init-replica-set.js:z \
+	--name overleaf-mongo \
+	"--health-cmd=echo \"db.stats().ok\" | mongosh localhost:27017/test --quiet" \
+	--health-interval=10s \
+	--health-timeout=10s \
+	--health-retries=5 \
+	docker.io/library/mongo:8.0 \
+	--replSet overleaf
+ExecStop=/usr/bin/podman stop \
+	--ignore -t 10 \
+	--cidfile=%t/%n.ctr-id
+ExecStopPost=/usr/bin/podman rm \
+	-f \
+	--ignore -t 10 \
+	--cidfile=%t/%n.ctr-id
+Type=notify
+NotifyAccess=all
+
+[Install]
+WantedBy=default.target
+```
+
+The important line is:
+```
+	docker.io/library/mongo:8.0 \
+```
+Where MongoDB version is stated, originally it was 6.0.  
+When upgrading you need to follow these steps:  
++ bring the container down
++ change the systemd unit with the next release and reload systemd daemons
++ bring the container up
++ set feature compatibility in MongoDB to the version you upgraded to
++ repeat until you upgraded to the desired version
+
+With commands it gives the following:  
+```bash
+systemctl --user stop container-overleaf-mongo.service  # then change the unit file
+systemctl --user daemon-reload
+systemctl --user start container-overleaf-mongo.service
+podman exec -it overleaf-mongo mongosh --eval 'db.adminCommand({ getParameter: 1, featureCompatibilityVersion: 1 })'        # to see which version the feature compatibility is currently set to
+podman exec -it overleaf-mongo mongosh --eval 'db.adminCommand({ setFeatureCompatibilityVersion: "7.0", confirm: true })'   # to set the feature compatibility to another version (here 7.0)
+```
+Then I had to repeat the same steps to upgrade from 7.0 to 8.0.  
+
+
+## Command outputs
+
+Here are example outputs when running with `podman exec` commands in a MongoDB container:
+
+### 1. Getting MongoDB version (not the feature compatibility, only the version of MongoDB)
+
+Command:
+
+```bash
+podman exec overleaf-mongo mongod --version
+```
+Output:
+
+```js
+db version v7.0.26
+Build Info: {
+    "version": "7.0.26",
+    "gitVersion": "715b3bbc6c34cecc42ffc77ef77d24f71e240e94",
+    "openSSLVersion": "OpenSSL 3.0.2 15 Mar 2022",
+    "modules": [],
+    "allocator": "tcmalloc",
+    "environment": {
+        "distmod": "ubuntu2204",
+        "distarch": "x86_64",
+        "target_arch": "x86_64"
+    }
+}
+```
+In this case the major version is 7.0.  
+
+### 2. Getting feature compatibility version  
+
+Command:
+
+```bash
+podman exec -it overleaf-mongo mongosh --eval 'db.adminCommand({ getParameter: 1, featureCompatibilityVersion: 1 })'
+```
+Output:
+
+```js
+{
+  featureCompatibilityVersion: { version: '6.0' },
+  ok: 1,
+  '$clusterTime': {
+    clusterTime: Timestamp({ t: 1763739555, i: 108 }),
+    signature: {
+      hash: Binary.createFromBase64('AAAAAAAAAAAAAAAAAAAAAAAAAAA=', 0),
+      keyId: Long('0')
+    }
+  },
+  operationTime: Timestamp({ t: 1763739555, i: 108 })
+}
+```
+Here we can see that the feature compatibility version is 6.0 (even though MongoDB was at version 7.0).  
+
+### 3. Upgrading feature compatibility version
+
+If we simply run:
+
+```bash
+podman exec -it overleaf-mongo mongosh --eval 'db.adminCommand({ setFeatureCompatibilityVersion: "7.0" })'
+```
+Then MongoDB gives us this warning (downgrades are not possible):
+
+```
+MongoServerError: Once you have upgraded to 7.0, you will not be able to downgrade FCV and binary version without support assistance. Please re-run this command with 'confirm: true' to acknowledge this and continue with the FCV upgrade.
+```
+
+If we indeed want to upgrade we need to run this command:
+
+```bash
+podman exec -it overleaf-mongo mongosh --eval 'db.adminCommand({ setFeatureCompatibilityVersion: "7.0", confirm: true })'
+```
+
+And we should get an ouput like this:
+
+```js
+{
+  ok: 1,
+  '$clusterTime': {
+    clusterTime: Timestamp({ t: 1763739614, i: 2 }),
+    signature: {
+      hash: Binary.createFromBase64('AAAAAAAAAAAAAAAAAAAAAAAAAAA=', 0),
+      keyId: Long('0')
+    }
+  },
+  operationTime: Timestamp({ t: 1763739614, i: 2 })
+}
+```
+
+
+
+