A Jenkins pipeline unavoidably uses confidential information such as usernames and passwords which need to be protected from unauthorised access and alteration. Jenkins enables this by allowing the variables used in your pipeline definition (stored in the file Jenkinsfile) to be sourced from your Jenkins Credentials which are then accessed via properties on your Jenkins Agents. To be more explicit:
Location | JENKINSFILE | NODE VARIABLES | GLOBAL CREDENTIALS |
|---|---|---|---|
Contents | Names of NODE VARIABLES | Names of GLOBAL CREDENTIALS | The actual (potentially encrypted) values used at runtime |
Environment and Local Variables
Note that the Jenkins Credentials Binding Plugin is used to take the values of encrypted environment variables and place their values into variables within the scope of the pipeline step.
For Example:
withCredentials([
string(credentialsId: "${env.MY_ENVIRONMENT_VARIABLE}", variable: 'MY_LOCAL_VAR'),
])
Example
Jenkinsfile
This Jenkinsfile contains a reference to a variable ${env.MCIPASSWORD}
Node Variable
The reference ${env.MCIPASSWORD} is an environment variable which is one of the properties of a Jenkins Agent (sometimes referred to as a Jenkins Node) using to execute the relevant pipeline stage(s):
Node Properties for this Agent include the referenced Environment Variable:
See Using Jenkins Agents - Jenkins documentation
From the Jenkins documentation:
Environment variables defined here will be made available to every build executed by this agent, and will override any environment variables that have the same Name as those defined on the Configure System page.
Using the syntax $NAME or ${NAME} (%NAME% on Windows), these variables can be used in job configurations, or from process launched by a build.
Jenkins also supports a special syntax, BASE+EXTRA, which allows you to add multiple key-value pairs here, which will be prepended to an existing environment variable.
For example, if you have a machine which has PATH=/usr/bin, you could add to the standard path by defining an environment variable here, with the name PATH+LOCAL_BIN and value /usr/local/bin.
This would result in PATH=/usr/local/bin:/usr/bin being exported during builds executed on this machine. PATH+LOCAL_BIN=/usr/local/bin will also be exported.
Multiple entries are prepended to the "base" variable according to the alphabetical order of the "extra" part of the name.
If the Value is empty or whitespace-only, it will not be added to the environment, nor will it override or unset any environment variable with the same name that may already exist (e.g. a variable defined by the system).
Global Credentials
Jenkins Credentials may be of a variety of types, including…
Username with password
Docker Host Certificate Authentication
SSH Username with private key
Secret file
Secret text
Certificate
In this example the Node’s Environment Variable with the ID MCIPASSWORD has, in this example, the value demo115-MCIPassword which is actually the ID of a value in your Jenkins Credentials store (see below). You can see from the Key icon in the 'T' column that that these credentials are of the type Secret text.
Taking a look at the specified value reveals the actual value used by the Jenkins pipeline at runtime:
