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GlusterFS for Persistent Docker Volumes

docker-and-glusterfs-blog-header.jpg

1. Preparation

1.1 KVMs

6 KVMs

Hostname vCPUs Memory Swap IP OS sudoer Data Storage
gluster01 2 2G 0 192.168.122.191 CentOS 7 echo 100G, /data/brick1
gluster02 2 2G 0 192.168.122.192 CentOS 7 echo 100G, /data/brick1
gluster03 2 2G 0 192.168.122.193 CentOS 7 echo 100G, /data/brick1
minion01.k8s 2 8G 0 192.168.122.101 CentOS 7 echo
minion02.k8s 2 8G 0 192.168.122.102 CentOS 7 echo
minion03.k8s 2 8G 0 192.168.122.103 CentOS 7 echo
swarm-nodes
/etc/ansible/hosts
[swarm-nodes]
minion01.k8s
minion02.k8s
minion03.k8s

1.2 Installing GlusterFS and docker swarm

For installing GlusterFS, please refer to Install Glusterfs on Centos 7.

For getting started with docker warm, please refer to Getting started with docker swarm mode.

1.3 DNS via hosts file

From the host server

cat <<EOF > /tmp/add-hosts.sh
cat <<EEE >> /etc/hosts 
192.168.122.191 gluster01
192.168.122.192 gluster02
192.168.122.193 gluster03
EEE
EOF

ansible swarm-nodes -u echo -b -m script -a "/tmp/add-hosts.sh"

2. Creating a GlusterFS volume

2.1 Create and start a GlusterFS volume

From the host server

ansible gluster -u echo -b -m shell -a 'mkdir -p /data/brick1/gfs'

From gluster01

Create and start the replicated volume gfs:

sudo gluster volume create gfs replica 3 \
 gluster01:/data/brick1/gfs \
 gluster02:/data/brick1/gfs \
 gluster03:/data/brick1/gfs

sudo gluster volume start gfs

sudo gluster volume info gfs

2.2 Mount the gfs volume locally

On all Gluster hosts, mount the gfs volume locally.

From the host server

cat <<EOF > /tmp/mount-gfs.sh
mkdir -p /mnt/gfs

echo 'localhost:/gfs /mnt/gfs glusterfs defaults,_netdev 0 0' >> /etc/fstab
mount -a
EOF

ansible gluster -u echo -b -m script -a '/tmp/mount-gfs.sh'


cat <<EOF > /tmp/fix-mount.sh
mkdir -p /usr/local/sbin

cat <<EEE > /usr/local/sbin/check-gfs.sh
#!/bin/sh
while true; do
  df | grep /mnt/gfs > /dev/null
  if [[ \\\$? -eq 0 ]]; then
    exit 0
  fi

  sleep 3
  mount -a -t glusterfs
done  
EEE

chmod +x /usr/local/sbin/check-gfs.sh

cat <<EEE > /etc/systemd/system/glusterfsmounts.service 
[Unit]
Description=Glustermounting
Requires=glusterd.service

[Service]
Type=simple
RemainAfterExit=true
ExecStartPre=/usr/sbin/gluster volume status gfs
ExecStart=/usr/local/sbin/check-gfs.sh
Restart=on-failure
RestartSec=3

[Install]
WantedBy=multi-user.target
EEE

systemctl daemon-reload
systemctl enable glusterfsmounts
EOF

ansible gluster -u echo -b -m script -a '/tmp/fix-mount.sh'

On gluser01 server

$ df -h |grep gfs
localhost:/gfs           100G  1.1G   99G    2% /mnt/gfs

3. Install the GlusterFS volume plugin for Docker

The GlusterFS plugin for Docker must be installed across all Swarm nodes, one by one.

cat <<EOF > /tmp/gfs-plugin.sh
docker plugin install --alias glusterfs \
  mochoa/glusterfs-volume-plugin \
  --grant-all-permissions --disable

docker plugin set glusterfs SERVERS=gluster01,gluster02,gluster03
docker plugin enable glusterfs
EOF

ansible swarm-nodes -u echo -b -m script -a '/tmp/gfs-plugin.sh' 

4. Deploy a stack consisting of 1 simple service with a GlusterFS volume

4.1 Create a subdiectory at the root of the GlusterFS volume

From gluster01 server, create a subdirectory named vol1 at the root of the GlusterFS volume.

sudo mkdir -p /mnt/gfs/vol1

4.2 Deploy a stack

From any Swarm node, create a stack file named docker-compose.yml.

cat <<EOF > docker-compose.yml
version: "3.7"

services:
  foo:
    image: alpine
    command: ping localhost
    networks:
      - net
    volumes:
      - vol1:/tmp

networks:
  net:
    driver: overlay

volumes:
  vol1:
    driver: glusterfs
    name: "gfs/vol1"
EOF

Deploy the stack.

$ sudo docker stack deploy -c docker-compose.yml test
Creating network test_net
Creating service test_foo

Check the stack.

$ sudo docker stack list
NAME                SERVICES            ORCHESTRATOR
test                1                   Swarm

$ sudo docker stack services test
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
zer9ypz8ghqo        test_foo            replicated          1/1                 alpine:latest       

4.3 Write some test data to the docker volume backed by GlusterFS

  • STEP1. Find out which of the Swarm nodes the test_foo service is running on.
$ sudo docker service ps test_foo
ID                  NAME                IMAGE               NODE           DESIRED STATE       CURRENT STATE           ERROR               PORTS
beqjzsj3yznd        test_foo.1          alpine:latest       minion01.k8s   Running             Running 5 minutes ago         
  • STEP2. Switch to the terminal for that Swarm node and find the container ID of the test_foo service.
container_id=$(sudo docker ps | grep test_foo | awk '{print $1}')
  • STEP3. Exec into the container’s /bin/sh shell.
sudo docker exec -it $container_id /bin/sh
  • STEP4. Write some test data to /tmp

Write 1G of test data to /tmp.

/ # echo 'dd if=/dev/zero of=/tmp/test.bin bs=1024k count=1000' > test.sh
/ # time sh test.sh
1000+0 records in
1000+0 records out
real    0m 3.35s
user    0m 0.00s
sys 0m 1.02s

From any Gluster server (e.g. gluster01), list out the test data.

$ ls -lh /mnt/gfs/vol1/
-rw-r--r--. 1 root root 1000M Nov 30 12:26 test.bin

Reference


Last update: 2021-12-05
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