Docker Swarm

Master slave configurations
At least three masters(From two is okay)- Odd numbers for masters is recommended
A maximum of 7 master nodes is recommended by docker

Creating a swarm

Identify the master
initiaize the cluster
Chose an interface to advertise

bash

swarm init  --advertise-addr 192.168.56.1

Output:

Managers

Getting command to run as manager
bash-MANAGER1
```
docker swarm join-token manager
```

Promoting a worker node to manager

You can promote a node from a manager
bash-MASTER
```
docker node promote docker-node2
```
docker-node2 is the hostname of the node
To update the hostname
bash-NODE2
```
hostname master-3
```

Prevent manager from running services

Run the command from a manager
bash-MANAGER
```
docker node update --availability drain docker-master
```
docker-master is the hostname.

Note

If the cluster is left with less than half of the managers, reinitializing the swarm can fix it if bringing the managers back up is not possible.
command: docker swarm init --force-new-cluster --advertise-addr 192.168.56.1

Nodes

Getting command to run as manager
bash-MANAGER
```
docker swarm join-token worker
```
Listing
bash-MANAGER
```
docker node ls 
```
Leaving a swarm
bash-NODE
```
docker swarm leave
```
Takes some time to reflect on the master
Leaving
bash-MASTER
```
docker node rm bash-NODE
```

Secrets

printf "my super secret password" | docker secret create my_secret -

onakdyv307se2tl7nl20anokv

docker secret ls

ID                          NAME                CREATED             UPDATED
onakdyv307se2tl7nl20anokv   my_secret           6 seconds ago       6 seconds ago

Services

Two types of services

Replicated -
Global (Placed on every node, eg monitoring tools)