SafeKit quick installation guide with Docker (mirror.safe mirror module)

Overview of the solution

Installation on Linux

Package installation on Linux

Install the free version of SafeKit on 2 Linux nodes.

Note: the free trial includes all SafeKit features. At the end of the trial, you can activate permanent license keys without uninstalling the package.
After the download of safekit_xx.bin package, execute it to extract the rpm and the safekitinstall script and then execute the safekitinstall script
Answer yes to firewall automatic configuration
Set the password for the web console and the default user admin.

Set the same password on all nodes.

Example 1 with a Docker compose application

With a Docker compose application, you have a docker-compose.yml file describing the application and all its containers.

First, on both servers, install the docker compose application without starting it: docker-compose -f docker-compose.yml up --no-start
On one server, for each volume in docker-compose.yml, run this command: docker volume inspect volume_name
It will return the host directories of the docker volumes (these paths are not given in docker-compose.yml).
You will get a list of paths as /var/lib/docker/volumes/<volume_name>/_data
Go to the step-by-step configuration section and
- deploy the mirror.safe module
- set a virtual IP address that will be switched in case of failure
- set the list of /var/lib/docker/volumes/<volume_name>/_data as replicated directories
- put respectively in start_prim and stop_prim scripts: /usr/local/bin/docker-compose -f docker-compose.yml --no-ansi start and /usr/local/bin/docker-compose -f docker-compose.yml --no-ansi stop

Example 2 with a Docker application starting a set of containers

We suppose here a Docker application myappli starting a set of containers.

First, on both servers, install myappli without starting it
On one server, list volumes used by myapply: ls /var/lib/docker/volumes
Thus, you will get a list of paths as /var/lib/docker/volumes/<volume_name>/_data
Go to the step-by-step configuration section and
- deploy the mirror.safe module
- set a virtual IP address that will be switched in case of failure
- set the list of /var/lib/docker/volumes/<volume_name>/_data as replicated directories
- put respectively in start_prim and stop_prim scripts: /.../myappli start and /.../myappli stop

Example 3 with a simple Docker image

The configuration is presented on the example of the nginx Docker image (web server).

Docker volume creation
On both servers, create a docker volume with the same name: docker volume create replicated_vol
Get the directory path where the volume is stored on the host: docker volume inspect replicated_vol
(for example : /var/lib/docker/storage/replicated_vol/_data)
Docker container creation
On both servers, create a nginx docker container that bind to the previous volume: docker container create --name mynginx -v replicated_vol:/usr/share/nginx/html -p 9011:80 nginx
Populate the volume with some index.html file: docker cp index.html mynginx:/usr/share/nginx/html/index.html
Go to the step-by-step configuration section and
- deploy the mirror.safe module
- set a virtual IP address that will be switched in case of failure
- set /var/lib/docker/storage/replicated_vol/_data as a replicated directory
- put respectively in start_prim and stop_prim scripts: docker start mynginx and docker stop mynginx
- after SafeKit configuration, test access to index.html with http://vitual-ip:9011

Step by step configuration

2. Configure node addresses

Enter the node IP addresses, press the Tab key to check connectivity and fill node names.
Then, click on Save and apply to save the configuration.

If either node1 or node2 has a red color, check connectivity of the browser to both nodes and check firewall on both nodes for troubleshooting.

If you want, you can add a new LAN for a second heartbeat and for a dedicated replication network.

If you click on Advanced configuration, the cluster.xml file is displayed. This file, automatically populated by the console, is the one that will be deployed on the nodes.

4. Configure the module

In Module startup at boot, choose an automatic start of the module at boot without delay.
In Macros / SERVICES, enter the service names of your application, in the startup order, separated by commas. See this screenshot for a visual example of Milestone XProtect services.
In Heartbeat networks, you should have a single heartbeat network on which the replication is made. If you have added a private LAN at step 2, then you can configure two heartbeats with the replication flow on the private LAN.
In Virtual IP addresses, enter a virtual IP address. A virtual IP address is a standard IP address in the same IP network (same subnet) as the IP addresses of both nodes.
Application clients must be configured with the virtual IP address (or the DNS name associated with the virtual IP address).
The virtual IP address is automatically switched in the event of a failure.
In Replicated directories, set the paths of directories to replicate. Check that they exist on both nodes and contain the application data.
Data and log replication are essential for a database.
You can create additional replicated directories as required.
See this screenshot for a visual example of Milestone XProtect SQL replication.
In Checkers, you will be able to configure checkers if needed, such as process monitoring, custom checkers, TCP, ping, or split-brain checkers.
For example, if a process name is displayed in Monitored processes/services, it will be monitored with a restart action in case of failure. Configuring a wrong process name will cause the module to stop right after its start.

If you click on Advanced configuration, the userconfig.xml file is displayed. This file, automatically populated by the console, is the one that will be deployed on the nodes along with the restart scripts.

5. Edit scripts (optional)

This step is optional and can be skipped in most cases, as the restart scripts are already pre-configured to restart services defined in the previous step.
So, click directly on Next step.
start_prim.ps1 starts all services in the order specified in the SERVICES list, while stop_prim.ps1 stops all services in the reverse order.
Additionally, start_prim.ps1 checks the startup of each service and stops the module if any service fails to start correctly.
During module configuration, the boot startup of services will automatically be set to ‘Manual’. This ensures that services do not start automatically upon system boot, but instead, they will be initiated only when the module itself is started.

9. Start the node with up-to-date data

If node 1 has the up-to-date replicated directories, select it and start it As primary.

When node 2 will be started, all data will be copied from node 1 to node 2.

If you make the wrong choice, you run the risk of synchronizing outdated data on both nodes.

It is also assumed that the Docker application is stopped on node 1 so that SafeKit installs the replication mechanisms and then starts the application in the start_prim script.

Use Start for subsequent starts: SafeKit retains the most up-to-date server. Starting As primary is a special start-up the first time or during exceptional operations.

10. Wait for the transition to ALONE (green)

Node 1 should reach the ALONE (green) state, which means that the virtual IP is set and that the start_prim script has been executed on node 1.

If ALONE (green) is not reached or if the application is not started, analyze why with the module log of node 1.

click the "log" icon of node1 to open the module log and look for error messages such as a checker detecting an error and stopping the module.
click on start_prim in the log: output messages of the script are displayed on the right and errors can be detected such as a service incorrectly started.

If the cluster is in WAIT (red) not uptodate, STOP (red) not uptodate state, stop the WAIT node and force its start as primary.

13. Testing

Stop the PRIM node by scrolling down its contextual menu and clicking Stop.
Verify that there is a failover on the SECOND node which should become ALONE (green).
And with Microsoft Management Console (MMC) on Windows or with command lines on Linux, check the failover of Docker services (stopped on node 1 in the stop_prim script and started on node 2 in the start_prim script).

If ALONE (green) is not reached on node2 or if the application is not started, analyze why with the module log of node 2.

click the "log" icon of node2 to open the module log and look for error messages such as a checker detecting an error and stopping the module.
click on start_prim in the log: output messages of the script are displayed on the right and errors can be detected such as a service incorrectly started.

If everything is okay, initiate a start on node1, which will resynchronize the replicated directories from node2.

If things go wrong, stop node2 and force the start as primary of node1, which will restart with its locally healthy data at the time of the stop.

Find more details, along with videos, in the SafeKit Online Training.