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ACI Lint

acilint is a static analysis tool for Cisco ACI fabrics. Some example use cases for such a tool include the following:

  • Configuration Analysis

    In this purpose, it can be used to examine the APIC configuration and determine whether any of the configuration could be possibly problematic or suspicious. It examines the configuration much like static code analysis tools such as the original lint checker did for software development in C or pylint for Python. It generates Warnings and Errors that give indications that the configuration should be examined. Often these Warnings are not problems, but incomplete or stale configuration that is not currently in use.

  • Compliance, Governance, and Auditing

    In this purpose, it can be used to determine whether the configuration meets higher level goverance and compliance rules. These rules are similar to lint style rules but exploit the APIC ability to provide additional classification tags on objects. Tags provide a simple and flexible way to classify any APIC object in one or more user-defined groups.

    For example, EPGs can be tagged as secure and non-secure. A compliance rule can be defined that specifies that secure EPGs cannot consume a contract from a non-secure EPG. Upon violation of this rule, a warning or an error can be raised.

Usage

acilint can be run against the current running APIC configuration or a previously saved set of configuration snapshot files.

Running using Live APIC configuration

When acilint collects the configuration directly from the APIC, it needs the proper login credentials. These can be passed via the command line arguments, a credentials.py file, environment variables, or if none of these, the user will be directly queried.

The following example shows how to run using the command line arguments for credentials:

python acilint.py -l admin -p password -u https://1.2.3.4

where admin is the APIC login username, password is the APIC password, and https://1.2.3.4 is the URL used to login to the APIC.

Running using Configuration Snapshot files

The snapback application provides the ability to save snapshots of the APIC configuration into JSON files. acilint can use these snapshot files as input rather than connecting to a live APIC.

This can be useful in debugging as it lets the user compare the acilint output of the live APIC to the output of a previous configuration snapshot. acilint can also be used to perform some "What If" scenarios. A single configuration snapshot actually consists of multiple snapshot files. These configuration files are then fed as input into acilint. These snapshot files fed into acilint can actually be from different configuration snapshot versions creating an entirely new configuration that may have never existed on the APIC, but we can run acilint against this configuration to check for possible errors and warnings that would occur if this configuration were to be deployed.

The following example shows how to run with configuration snapahot files as input:

python acilint.py --snapshotfiles infra.json tenant-cisco.json fabric.json

Customization

By default, all checks will be performed. However, like many static code analysis tools, acilint is customizable and only the desired warnings and errors can be issued.

To customize acilint, generate a configuration file with the following command:

python acilint.py --generateconfigfile acilint.cfg

or even shorter:

python acilint.py -g acilint.cfg

where acilint.cfg is the filename you wish to create.

The generated configuration file will contain a list of all of the current checks being performed.

An example config file is shown below:

# acilint configuration file
# Remove or comment out any warnings or errors that you no longer wish to see
 error_001
 error_002
 warning_001
 warning_002
 warning_003

To remove checks, either:

  • Delete the line containing the check, or
  • Comment it out by prepending a # in front of the check

Errors and Warnings

The following list of Errors and Warnings are performed by acilint. Since acilint is written on top of the acitoolkit package, the checks are limited to the functionality exposed by that package. However as the acitoolkit expands, so shall acilint.

Warnings

warning_001 Tenant has no app profile
warning_002 Tenant has no context
warning_003 AppProfile has no EPGs
warning_004 Context has no BridgeDomain
warning_005 BridgeDomain has no EPGs assigned
warning_006 Contract is not provided at all
warning_007 Contract is not consumed at all
warning_008 EPG providing contracts but in a Context with no enforcement
warning_010 EPG providing contract but consuming EPG is in a different context
warning_011 Contract contains bi-directional TCP Subjects
warning_012 Contract contains bi-directional UDP Subjects
warning_013 Contract has no Subjects
warning_014 Contract has Subjects with no Filters

Errors

error_001 BridgeDomain has no context
error_002 EPG has no BD assigned
error_005 Duplicate or overlapping subnets in Context
error_006 ExternalNetwork Subnets duplicated in fabric

Critical

critical_001 Compliance check example

critical_001 is a compliance check example that will perform the following:

  • Ensure that all of the EPGs in the system have been classified as secure and nonsecure using the tagging capability provided by the acitoolkit.
  • Ensures that none of the secure EPGs can communicate with the nonsecure EPGs by checking that no contract provided by secure EPGs is consumed by nonsecure EPGs.

Developing Checks

Additional checks can be added through new methods on the Checker class. If the method begins with warning_ or error_ or critical_, it will automatically be executed as part of the acilint execution. The new checks will also automatically inherit the customization capability through the usage of the configuration file. Some familiarity with the acitoolkit object model is necessary to write additional checks.