Cisco ACI Guide

What is Cisco ACI ?

Application Centric Infrastructure (ACI)

The Cisco Application Centric Infrastructure (ACI) allows application requirements to define the network. This architecture simplifies, optimizes, and accelerates the entire application deployment life cycle.

Application Policy Infrastructure Controller (APIC)

The APIC manages the scalable ACI multi-tenant fabric. The APIC provides a unified point of automation and management, policy programming, application deployment, and health monitoring for the fabric. The APIC, which is implemented as a replicated synchronized clustered controller, optimizes performance, supports any application anywhere, and provides unified operation of the physical and virtual infrastructure.

The APIC enables network administrators to easily define the optimal network for applications. Data center operators can clearly see how applications consume network resources, easily isolate and troubleshoot application and infrastructure problems, and monitor and profile resource usage patterns.

The Cisco Application Policy Infrastructure Controller (APIC) API enables applications to directly connect with a secure, shared, high-performance resource pool that includes network, compute, and storage capabilities.

ACI Fabric

The Cisco Application Centric Infrastructure (ACI) Fabric includes Cisco Nexus 9000 Series switches with the APIC to run in the leaf/spine ACI fabric mode. These switches form a “fat-tree” network by connecting each leaf node to each spine node; all other devices connect to the leaf nodes. The APIC manages the ACI fabric.

The ACI fabric provides consistent low-latency forwarding across high-bandwidth links (40 Gbps, with a 100-Gbps future capability). Traffic with the source and destination on the same leaf switch is handled locally, and all other traffic travels from the ingress leaf to the egress leaf through a spine switch. Although this architecture appears as two hops from a physical perspective, it is actually a single Layer 3 hop because the fabric operates as a single Layer 3 switch.

The ACI fabric object-oriented operating system (OS) runs on each Cisco Nexus 9000 Series node. It enables programming of objects for each configurable element of the system. The ACI fabric OS renders policies from the APIC into a concrete model that runs in the physical infrastructure. The concrete model is analogous to compiled software; it is the form of the model that the switch operating system can execute.

All the switch nodes contain a complete copy of the concrete model. When an administrator creates a policy in the APIC that represents a configuration, the APIC updates the logical model. The APIC then performs the intermediate step of creating a fully elaborated policy that it pushes into all the switch nodes where the concrete model is updated.

The APIC is responsible for fabric activation, switch firmware management, network policy configuration, and instantiation. While the APIC acts as the centralized policy and network management engine for the fabric, it is completely removed from the data path, including the forwarding topology. Therefore, the fabric can still forward traffic even when communication with the APIC is lost.

More information

Various resources exist to start learning ACI, here is a list of interesting articles from the community.

Using the ACI modules

The Ansible ACI modules provide a user-friendly interface to managing your ACI environment using Ansible playbooks.

For instance ensuring that a specific tenant exists, is done using the following Ansible task using module aci_tenant <aci_tenant_module>:

- name: Ensure tenant customer-xyz exists
    host: my-apic-1
    username: admin
    password: my-password

    tenant: customer-xyz
    description: Customer XYZ
    state: present

A complete list of existing ACI modules is available for the latest stable release as well as the current development version.

Querying ACI configuration

A module can also be used to query a specific object.

- name: Query tenant customer-xyz
    host: my-apic-1
    username: admin
    password: my-password

  tenant: customer-xyz
  state: query

Or query all objects.

- name: Query all tenants
    host: my-apic-1
    username: admin
    password: my-password

    state: query
  register: all_tenants

After registering the return values of the aci_tenant <aci_tenant_module> task as shown above, you can access all tenant information from variable all_tenants.

Common parameters

Every Ansible ACI module accepts the following parameters that influence the module’s communication with the APIC REST API:

Hostname or IP address of the APIC.
Port to use for communication. (Defaults to 443 for HTTPS, and 80 for HTTP)
User name used to log on to the APIC. (Defaults to admin)
Password for username to log on to the APIC, using password-based authentication.
Private key for username to log on to APIC, using signature-based authentication. New in version 2.5
Name of the certificate in the ACI Web GUI. (Defaults to private_key file base name) New in version 2.5
Timeout value for socket-level communication.
Use system proxy settings. (Defaults to yes)
Use HTTPS or HTTP for APIC REST communication. (Defaults to yes)
Validate certificate when using HTTPS communication. (Defaults to yes)
Influence the level of detail ACI modules return to the user. (One of normal, info or debug) New in version 2.5

Proxy support

By default, if an environment variable <protocol>_proxy is set on the target host, requests will be sent through that proxy. This behaviour can be overridden by setting a variable for this task (see Setting the Environment (and Working With Proxies)), or by using the use_proxy module parameter.

HTTP redirects can redirect from HTTP to HTTPS so you should be sure that your proxy environment for both protocols is correct.

If you don’t need proxy support, but the system may have it configured nevertheless, you can add this parameter setting: use_proxy: no to avoid accidental proxy usage.


Selective proxy support using the no_proxy environment variable is also supported.

Return values

New in version 2.5.

The following values are always returned:

The resulting state of the managed object, or results of your query.

The following values are returned when output_level: info:

The original state of the managed object (before any change was made).
The proposed config payload, based on user-supplied values.
The sent config payload, based on user-supplied values and the existing configuration.

The following values are returned when output_level: debug or ANSIBLE_DEBUG=1:

The filter used for specific APIC queries.
The HTTP method used for the sent payload. (Either GET for queries, DELETE or POST for changes)
The HTTP response from the APIC.
The HTTP status code for the request.
The url used for the request.


The module return values are documented in detail as part of each module’s documentation.

More information

Various resources exist to start learn more about ACI programmability, we recommend the following links:

ACI authentication

Password-based authentication

If you want to log on using a username and password, you can use the following parameters with your ACI modules:

username: admin
password: my-password

Password-based authentication is very simple to work with, but it is not the most efficient form of authentication from ACI’s point-of-view as it requires a separate login-request and an open session to work. To avoid having your session time-out and requiring another login, you can use the more efficient Signature-based authentication.


Password-based authentication also may trigger anti-DoS measures in ACI v3.1+ that causes session throttling and results in HTTP 503 errors and login failures.


Never store passwords in plain text.

The “Vault” feature of Ansible allows you to keep sensitive data such as passwords or keys in encrypted files, rather than as plain text in your playbooks or roles. These vault files can then be distributed or placed in source control. See Using Vault in playbooks for more information.

Signature-based authentication using certificates

New in version 2.5.

Using signature-based authentication is more efficient and more reliable than password-based authentication.

Generate certificate and private key

Signature-based authentication requires a (self-signed) X.509 certificate with private key, and a configuration step for your AAA user in ACI. To generate a working X.509 certificate and private key, use the following procedure:

$ openssl req -new -newkey rsa:1024 -days 36500 -nodes -x509 -keyout admin.key -out admin.crt -subj '/CN=Admin/O=Your Company/C=US'

Configure your local user

Perform the following steps:

  • Add the X.509 certificate to your ACI AAA local user at ADMIN » AAA
  • Click AAA Authentication
  • Check that in the Authentication field the Realm field displays Local
  • Expand Security Management » Local Users
  • Click the name of the user you want to add a certificate to, in the User Certificates area
  • Click the + sign and in the Create X509 Certificate enter a certificate name in the Name field
    • If you use the basename of your private key here, you don’t need to enter certificate_name in Ansible
  • Copy and paste your X.509 certificate in the Data field.

You can automate this by using the following Ansible task:

- name: Ensure we have a certificate installed
    host: my-apic-1
    username: admin
    password: my-password

    aaa_user: admin
    certificate_name: admin
    certificate: "{{ lookup('file', 'pki/admin.crt') }}"  # This wil read the certificate data from a local file


Signature-based authentication only works with local users.

Use signature-based authentication with Ansible

You need the following parameters with your ACI module(s) for it to work:

username: admin
private_key: pki/admin.key
certificate_name: admin  # This could be left out !


If you use a certificate name in ACI that matches the private key’s basename, you can leave out the certificate_name parameter like the example above.

More information

Detailed information about Signature-based Authentication is available from Cisco APIC Signature-Based Transactions.

Using ACI REST with Ansible

While already a lot of ACI modules exists in the Ansible distribution, and the most common actions can be performed with these existing modules, there’s always something that may not be possible with off-the-shelf modules.

The aci_rest module provides you with direct access to the APIC REST API and enables you to perform any task not already covered by the existing modules. This may seem like a complex undertaking, but you can generate the needed REST payload for any action performed in the ACI web interface effortlessly.

Built-in idempotency

Because the APIC REST API is intrinsically idempotent and can report whether a change was made, the aci_rest module automatically inherits both capabilities and is a first-class solution for automating your ACI infrastructure. As a result, users that require more powerful low-level access to their ACI infrastructure don’t have to give up on idempotency and don’t have to guess whether a change was performed when using the aci_rest module.

Using the aci_rest module

The aci_rest module accepts the native XML and JSON payloads, but additionally accepts inline YAML payload (structured like JSON). The XML payload requires you to use a path ending with .xml whereas JSON or YAML require the path to end with .json.

When you’re making modifications, you can use the POST or DELETE methods, whereas doing just queries require the GET method.

For instance, if you would like to ensure a specific tenant exists on ACI, these below four examples are functionally identical:


- aci_rest:
    host: my-apic-1
    private_key: pki/admin.key

    method: post
    path: /api/mo/uni.xml
    content: |
      <fvTenant name="customer-xyz" descr="Customer XYZ"/>


- aci_rest:
    host: my-apic-1
    private_key: pki/admin.key

    method: post
    path: /api/mo/uni.json
        "fvTenant": {
          "attributes": {
            "name": "customer-xyz",
            "descr": "Customer XYZ"

YAML (Ansible-style REST)

- aci_rest:
    host: my-apic-1
    private_key: pki/admin.key

    method: post
    path: /api/mo/uni.json
          name: customer-xyz
          descr: Customer XYZ

Ansible task (Dedicated module)

- aci_tenant:
    host: my-apic-1
    private_key: pki/admin.key

    tenant: customer-xyz
    description: Customer XYZ
    state: present


The XML format is more practical when there is a need to template the REST payload (inline), but the YAML format is more convenient for maintaing your infrastructure-as-code and feels more naturely integrated with Ansible playbooks. The dedicated modules offer a more simple, abstracted, but also a more limited experience. Use what feels best for your use-case.

More information

Plenty of resources exist to learn about ACI’s APIC REST interface, we recommend the links below:

Operational examples

Here is a small overview of useful operational tasks to reuse in your playbooks.

Feel free to contribute more useful snippets.

Waiting for all controllers to be ready

You can use the below task after you started to build your APICs and configured the cluster to wait until all the APICs have come online. It will wait until the number of controllers equals the number listed in the apic inventory group.

- name: Waiting for all controllers to be ready
    host: '{{ apic_ip }}'
    private_key: pki/admin.key
    method: get
    path: /api/node/class/topSystem.json?query-target-filter=eq(topSystem.role,"controller")
  register: topsystem
  until: topsystem|success and topsystem.totalCount|int >= groups['apic']|count >= 3
  retries: 20
  delay: 30

Waiting for cluster to be fully-fit

The below example waits until the cluster is fully-fit. In this example you know the number of APICs in the cluster and you verify each APIC reports a ‘fully-fit’ status.

- name: Waiting for cluster to be fully-fit
    host: '{{ apic_ip }}'
    private_key: pki/admin.key
    method: get
    path: /api/node/class/infraWiNode.json?query-target-filter=wcard(infraWiNode.dn,"topology/pod-1/node-1/av")
  register: infrawinode
  until: >
    infrawinode|success and
    infrawinode.totalCount|int >= groups['apic']|count >= 3 and
    infrawinode.imdata[0] == 'fully-fit' and
    infrawinode.imdata[1] == 'fully-fit' and
    infrawinode.imdata[2] == 'fully-fit'
#    all( == 'fully-fit' for apic in infrawinode.imdata)
  retries: 30
  delay: 30

APIC error messages

The following error messages may occur and this section can help you understand what exactly is going on and how to fix/avoid them.

APIC Error 122: unknown managed object class ‘polUni’
In case you receive this error while you are certain your aci_rest payload and object classes are seemingly correct, the issue might be that your payload is not in fact correct JSON (e.g. the sent payload is using single quotes, rather than double quotes), and as a result the APIC is not correctly parsing your object classes from the payload. One way to avoid this is by using a YAML or an XML formatted payload, which are easier to construct correctly and modify later.
APIC Error 400: invalid data at line ‘1’. Attributes are missing, tag ‘attributes’ must be specified first, before any other tag
Although the JSON specification allows unordered elements, the APIC REST API requires that the JSON attributes element precede the children array or other elements. So you need to ensure that your payload conforms to this requirement. Sorting your dictionary keys will do the trick just fine. If you don’t have any attributes, it may be necessary to add: attributes: {} as the APIC does expect the entry to precede any children.
APIC Error 801: property descr of uni/tn-TENANT/ap-AP failed validation for value ‘A “legacy” network’
Some values in the APIC have strict format-rules to comply to, and the internal APIC validation check for the provided value failed. In the above case, the description parameter (internally known as descr) only accepts values conforming to Regex: [a-zA-Z0-9\!#$%()*,-./:;@ _{|}~?&+]+, in general it must not include quotes or square brackets.

Known issues

The aci_rest module is a wrapper around the APIC REST API. As a result any issues related to the APIC will be reflected in the use of this module.

All below issues either have been reported to the vendor, and most can simply be avoided.

Too many consecutive API calls may result in connection throttling

Starting with ACI v3.1 the APIC will actively throttle password-based authenticated connection rates over a specific treshold. This is as part of an anti-DDOS measure but can act up when using Ansible with ACI using password-based authentication. Currently, one solution is to increase this treshold within the nginx configuration, but using signature-based authentication is recommended.

NOTE: It is advisable to use signature-based authentication with ACI as it not only prevents connection-throttling, but also improves general performance when using the ACI modules.

Specific requests may not reflect changes correctly (#35401)

There is a known issue where specific requests to the APIC do not properly reflect changed in the resulting output, even when we request those changes explicitly from the APIC. In one instance using the path api/node/mo/uni/infra.xml fails, where api/node/mo/uni/infra/.xml does work correctly.

NOTE: A workaround is to register the task return values (e.g. register: this) and influence when the task should report a change by adding: changed_when: this.imdata != [].

Specific requests are known to not be idempotent (#35050)

The behaviour of the APIC is inconsistent to the use of status="created" and status="deleted". The result is that when you use status="created" in your payload the resulting tasks are not idempotent and creation will fail when the object was already created. However this is not the case with status="deleted" where such call to an non-existing object does not cause any failure whatsoever.

NOTE: A workaround is to avoid using status="created" and instead use status="modified" when idempotency is essential to your workflow..

Setting user password is not idempotent (#35544)

Due to an inconsistency in the APIC REST API, a task that sets the password of a locally-authenticated user is not idempotent. The APIC will complain with message Password history check: user dag should not use previous 5 passwords.

NOTE: There is no workaround for this issue.

ACI Ansible community

If you have specific issues with the ACI modules, or a feature request, or you like to contribute to the ACI project by proposing changes or documentation updates, look at the Ansible Community wiki ACI page at:

You will find our roadmap, an overview of open ACI issues and pull-requests and more information about who we are. If you have an interest in using ACI with Ansible, feel free to join ! We occasionally meet online to track progress and prepare for new Ansible releases.

See also

Ansible for Network Automation
A detailed guide on how to use Ansible for automating network infrastructure.
List of ACI modules
A complete list of supported ACI modules.
ACI community
The Ansible ACI community wiki page, includes roadmap, ideas and development documentation.
Network Working Group
The Ansible Network community page, includes contact information and meeting information.
The #ansible-network IRC chat channel on
User Mailing List
Have a question? Stop by the google group!