casper-node-launcher

A binary which runs and upgrades the casper-node of the Casper network.

Usage

    casper-node-launcher [OPTIONS]

OPTIONS:
    -f, --force-version <version>    Forces the launcher to run the specified version of the node,
                                     for example "1.2.3"
    -h, --help                       Print help information
    -V, --version                    Print version information

On startup, launcher checks whether the installed node binaries match the installed configs, by comparing the version numbers. If not, it exits with an error.

The launcher then checks if the --force-version parameter was provided. If yes, it will unconditionally run the specified node, given it is installed. The requested version is then cached in the state, so the subsequent runs of the launcher will continue to execute the previously requested version.

If the --force-version parameter was not provided the launcher either tries to read its previously cached state from disk, or assumes a fresh start. On a fresh start, the launcher searches for the highest installed version of casper-node and starts running it in validator mode.

After every run of the casper-node binary in validator mode, the launcher does the following based upon the exit code returned by casper-node:

If 0 (success), searches for the immediate next installed version of casper-node and runs it in migrate-data mode
If 102 (downgrade), searches for the immediate previous installed version of casper-node and runs it in validator mode
Any other value causes the launcher to exit with an error

After every run of the casper-node binary in migrate-data mode, the launcher does the following based upon the exit code returned by casper-node:

If 0 (success), runs the same version of casper-node in validator mode
If 102 (downgrade), searches for the immediate previous installed version of casper-node and runs it in validator mode
Any other value causes the launcher to exit with an error

If the launcher cannot find an appropriate version at any stage of upgrading or downgrading, it exits with an error.

The default path for the casper-node's config file is /etc/casper/1_0_0/config.toml where the folder 1_0_0 indicates the semver version of the node software.

The default path for the launcher's cached state file is /etc/casper/casper-node-launcher-state.toml.

For testing purposes, the common folder /etc/casper can be overridden by setting the environment variable CASPER_CONFIG_DIR to a different folder.

The default path for the casper-node binary is /var/lib/casper/bin/1_0_0/casper-node where the folder 1_0_0 likewise indicates the version. The default path for the casper-node-launcher binary is /var/lib/casper/bin/casper-node-launcher.

For testing purposes, the common folder /var/lib/casper/bin can be overridden by setting the environment variable CASPER_BIN_DIR to a different folder.

Number of Files Limit

When casper-node launches, it tries to set the nofiles for the process to 64000. With some systems, this will hit the default hard limit of 4096.

Filehandles are used for both files and network connections. The network connections are unpredictable and running out of file handles can stop critical file writes from occurring. This limit may need to be increased from defaults.

With casper-node-launcher running we can see what the system allocated by finding our process id (PID) for casper-node with pgrep "casper-node$".

$ pgrep "casper-node$"
275928

This PID will change so you need to run the above command to get the current version with your system.
It will not be 275928 each time. If you get no return, you do not have casper-node-launcher running properly.

To find the current nofile (number of open files) hard limit, we can run prlimit with this PID:

$ sudo prlimit -n -p 275928
RESOURCE DESCRIPTION              SOFT HARD UNITS
NOFILE   max number of open files 1024 4096 files

We can embed both commands together so it is only sudo prlimit -n -p $(pgrep "casper-node$").

$ sudo prlimit -n -p $(pgrep "casper-node$")
RESOURCE DESCRIPTION              SOFT HARD UNITS
NOFILE   max number of open files 1024 4096 files

If you receive prlimit: option requires an argument -- 'p' with the above command then pgrep "casper-node$" is not returning anything because casper-node is no longer running.

Manual increase

This is how you set nofile for an active process. It will make sure you don't have issues without having to restart the casper-node-launcher and your node's casper-node process.

We run sudo prlimit --nofile=64000 --pid=$(pgrep "casper-node$").

After this when we look at prlimit it should show the change:

$ sudo prlimit -n -p $(pgrep "casper-node$")
RESOURCE DESCRIPTION               SOFT  HARD UNITS
NOFILE   max number of open files 64000 64000 files

This is only active while the casper-node process is active and therefore will not persist across server reboots, casper-node-launcher restarts, and protocol upgrades. We need to do something else to make this permanent.

limits.conf

Adding the nofile setting for casper user in /etc/security/limits.conf will persist this value.

Add:

casper hard nofile 64000

to the bottom of /etc/security/limits.conf.

After doing this you need to log out of any shells you have to enable this change. Restarting the node should maintain the correct nofile setting.

systemd unit modification (bad alternative)

When casper-node-launcher is installed, /lib/systemd/system/casper-node-launcher.service is created.
Inside this file, a line is provided which will allow systemd to increase the nofile setting at launch.

#LimitNOFILE=64000

Editing this file with sudo will allow you to uncomment this line and save. After saving you would need to run sudo systemctl daemon-reload to reload your changes. Then you would need to restart casper-node-launcher.