Introduction

• The JITL SSHJob implements an SSH client (Secure Shell) and allows execution of shell code, scripts and programs on a remote host without a JS7 Agent being installed on that host. As a prerequisite the remote host has to operate a standard-compliant SSH server.

• The SSHJob allows execution of commands, scripts, executables on remote Unix and Windows systems.

  • Unix based operating systems generally provide an SSH client, while Windows operating systems by default do not.
• The beauty of SSH is its simplicity. It allows public/private key authentication and is well suited to execution of programs for specific accounts.
• The JITL SSHJob allows shell scripts to add return values to orders.
• One of the restrictions of SSH connections is that there is limited control of child processes on the remote host. 
  • If a number of child processes are spawned by a program during an SSH session and that session is aborted then child processes will continue to run.
  • The SSHJob provides a means of controlling this behavior with output to stderr and shell command exit codes.
• For Windows operating systems hardly any products are available with decent SSH server capabilities and therefore the use of JS7 Agents for Windows is preferable.

Usage

When defining the job consider:

• invoking the Wizard that is available from the job properties tab in the Configuration view and selecting the JITL SSHJob and relevant arguments from the Wizard

or 

• specifing the com.sos.jitl.jobs.ssh.SSHJob Java class name and then adding arguments as explained in the documentation below.

Example

Download (upload .json): jdSSHPublicKeyAuthentication.json

An SSHJob configuration can look like this:

The SSHJob arguments can look like this:

Explanation:

• The workflow implements two jobs:
  • Job: execute-ssh
    • Argument: command
      

      • The value of the argument is a number of shell commands:

        echo "printing environment variables"
        printenv
        echo "adding hostname $HOSTNAME to variable remote_hostname"
        echo "remote_hostname=$HOSTNAME" >> $JS7_RETURN_VALUES

        The last line appends a key=value pair to a temporary file that is made available from the JS7_RETURN_VALUES environment variable. The name being remote_hostname and the value being provided from the HOSTNAME environment variable.
        This creates an order variable with the name remote_hostname that is available to subsequent jobs and instructions in a workflow.

    • Argument: create_env_vars
      • The argument is assigned the value true that specifies that for any order variables the job will create environment variables in the remote session.
        • For example, an order variable with the name date will be made available from the environment variable JS7_VAR_DATE.
      • For details see chapter Variables.
    • For the full list of available arguments see next chapter.
  • Job: display-result
    • Argument: no arguments
    • Environment Variables
      • The job is assigned an environment variable with the name REMOTE_HOSTNAME and the value $remote_hostname which is a reference to the order variable created by the previous job.
    • Script

      • The job script looks like this:

        echo "using workflow: $JS7_WORKFLOW_NAME"
        echo "running job: $JS7_JOB_NAME"
        
        echo "remote hostname: $REMOTE_HOSTNAME"

        The job script makes use of the REMOTE_HOSTNAME environment variable that is populated from the order variable created by the previous job.

Documentation

The Job Documentation including the full list of arguments can be found under: https://www.sos-berlin.com/doc/JS7-JITL/SSHJob.xml

The most commonly used arguments are listed in the table below.

• Required Arguments
  • Arguments that have to be specified with the job configuration.
    • Example: The  host argument is required to run a job that connects to a remote host.
• Optional Arguments
  • Arguments that must not be provided or arguments that are technically required but are available from default values.
    • Example 1: technically required, but available from default value
      • To connect to a remote host, the  port argument is required. The argument is available from the default value 22, therefore the port argument is not required.
    • Example 2: not required
      • The proxy_host argument is used only if the job's connection makes use of a proxy.

The com.sos.jitl.jobs.ssh.SSHJJob class accepts the following arguments:

The SSHJob can be used with a credential store to hold sensitive arguments. For use of the credential_store_* arguments see JS7 - Use of Credential Store with JITL Jobs.

Variables

FEATURE AVAILABILITY STARTING FROM RELEASE 2.3.0

Forwarding Variables

The SSHJob has access to variables from the following sources:

• Global Variables
  • Sources
    • These variables are available from any Agent and are used to populate the remote shell.
    • For a full list see JS7 - Job Environment Variables, chapter: Environment Variables that are automatically available to Shell Jobs.
  • Mapping
    • Environment variables use the prefix JS7_.
• Specific Variables
  • Sources
    • Order variables that are added when planning or submitting an order.
    • Workflow variables that are added dynamically during execution of the workflow.
    • Job Resource variables that are added from JS7 - Job Resources at workflow level and at job level.
  • Mapping
    • Specific variables use names within the scope of the JS7 - Object Naming Rules and are mapped to environment variables in the remote SSH session:
    • Environment variables use the prefix JS7_VAR_.
    • If the same variable names are used in a number of sources then the following precedence applies:
      • order variables, workflow variables, job resource variables.
      • for job resource variables account is taken of the order of assignment of the job resource: a variable with the same name used by a previously assigned job resource will not be overwritten by a later job resource. Job resources assigned at workflow level take priority over job resources assigned at job level.

Examples:

• The global variable JS7_AGENT_TZ is available with the remote SSH session and indicates the JS7 Agent's local time zone.
• A specific variable $dbName is mapped to the environment variable JS7_VAR_DBNAME in the remote SSH session.
• A specific variable $ScriptDir is specified by a job resource with a value /usr/scripts and is declared with a workflow using the default value /var/scripts. The resulting environment variable JS7_VAR_SCRIPTDIR will hold the value /var/scripts unless a different value is specified by the order that is added to the workflow.

Passing back Variables

The command script or commands of the SSHJob executed on the remote host can pass back variables to the workflow. To this purpose the command script or commands append any number of key=value pairs to a temporary file that will be picked up by the SSHJob. Each key=value pair is passed back to the workflow and becomes an order variable.

Example:

The command 

echo MYPARAM=myTestValue >> $JS7_RETURN_VALUES

appends MYPARAM=myTestValue to the temporary file defined by the environment variable JS7_RETURN_VALUES. For Unix the environment variable is specified using $JS7_RETURN_VALUES, for Windows the syntax is %JS7_RETURN_VALUES%.

The JS7_RETURN_VALUES environment variable is made available by the SSHJob during job execution. When the SSHJob completes it will read the key=value pairs from the temporary file and will add them as order variables to the job's outcome. The order variable MYPARAM  can be used in subsequent jobs. When calling up the variable the syntax $MYPARAM is used for Unix and Windows. Users should consider case-sensitive spelling of order variables.

Cancellation

The following operations are available:

• The cancel operation is applied to the order, not to the SSHJob. In case of cancellation the job will continue until completion and the order will be put in the failed state.
• The cancel/kill operation is applied to the order and to the job. The SSHJob will be killed immediately, similarly child processes in the remote SSH session will be killed. The order will be put in the failed state.
  • For older SSH servers, for example OpenSSH before version 7.5, to kill child processes in the remote SSH session the simulate_shell job attribute has to be used.

Further Resources

• JS7 - JITL Common Variables
• JS7 - Job Resources
• JS7 - Use of Credential Store with JITL Jobs