Developing An Ansible Role for Nexus Repository Manager v3.x

This article aims to explain how to automate the installation as well as configuration of Nexus’s Repository Manager version 3.x with Ansible.

Ansible is a deployment tool, which enables playbooks to automate applications and infrastructure deployments. The key advantage is its flexibility to change applications with versatility as well as apprehending them as a service. However, Ansible has some weaknesses too. Following a voluntary simple design, it functions solely as an application of parameters without taking into account information availability and security concerns, which need to be handled by other systems. That is why developers will prefer to use Ansible in combination with a stateful agent system like Puppet, or a centralized management tool like Ansible Tower.

Automation with Ansible

Ansible focuses on the application-level setup, scripting a provisioning that can be run on top of any infrastructure-supporting tool (PaaS, containers, bare-metal, vagrant, etc.). It only needs an SSH connection and a sudo account to the remote system.

Provisioning scripts in Ansible are written in a declarative style using YAML files grouped as roles. The atomic instructions in those roles are expressed using a number of core modules provided by Ansible. Please have a look at the Ansible documentation for an in-depth introduction.

Re-provisioning and Updating Configuration

One of the DevOps’ models to handle configuration updates consists of provisioning a brand new environment from scratch and completely discarding the old one (think container images). This implies a reliable management of your data lifecycle. In our particular case of Nexus’s Repository Manager, this consists of several gigs of uploaded/proxied artifacts, some audit logs, and OrientDB blobs containing the configuration. Therefore, depending on one’s environment constraints, it can make sense to be able to update the configuration of an already-provisioned Nexus instance. The declarative nature of Ansible’s core instructions is inline with this purpose, but any custom logic written in a role should be idempotent, take the “create or maybe update” path into account.

One must also note that some parts of the Nexus configuration cannot be updated. Some examples include:

• the settings related to BlobStores
• the admin password if you ever loose the current one (update : or maybe through this way)

How to make Nexus’s Groovy API Fit Well with Ansible

The basic steps of the installation are pretty straightforward and can all be written using simple Ansible core modules:

• download and unpack the archive
• create a system user/group
• create a systemd service

(these steps are in tasks/nexus_install.yml)

And then comes the surprise: Nexus configuration is not available in a simple text file format which can be edited with the help of simple Ansible instructions. It is stored in an embedded OrientDB database that must not be altered directly. The documented way to setup Nexus is either through its web user interface, or through its Integration API.

The way the Integration API works is as follows:

1. Write a Groovy script that handles your configuration change;
2. Upload it to Nexus with an HTTP PUT request, creating a REST resource for this script;
3. Call the script through its HTTP GET/POST resource.

URI Module to the Rescue!

Ansible’s uri module makes HTTP requests, providing automation to all of this.

The first step is to upload the Groovy script on Nexus. Note that the script may already be there. Therefore, on re-runs of the playbook, we try to delete it before taking any action, just in case:

Through tasks/declare_script_each.yml, follow on:

  ---
  - name: Removing (potential) previously declared Groovy script {{</span> item }}
    uri:
      url: "http://localhost:8081/service/siesta/rest/v1/script/{{ item }}"
      user: 'admin'
      password: "{{ current_nexus_admin_password }}"
      method: DELETE
      force_basic_auth: yes
      status_code: 204,404

  - name: Declaring Groovy script {{ item }}
    uri:
      url: "http://localhost:8081/service/siesta/rest/v1/script"
      user: 'admin'
      password: "{{ current_nexus_admin_password }}"
      body_format: json
      method: POST
      force_basic_auth: yes
      status_code: 204
      body:
        name: "{{ item }}"
        type: 'groovy'
        content: "{{ lookup('template', 'groovy/' + item + '.groovy') }}"

The HTTP requests are executed from inside the target host, which is why localhost is used here. force_basic_auth: yes makes the HTTP client not wait for a 401 before providing credentials, as Nexus immediately replies with 403 when no credentials are passed. status_code is the expected HTTP status replied by Nexus. Since the Groovy script may not necessarily exist at that point, we must also accept the 404 status code.

The next step is to call the Groovy script that has been created through the previous HTTP call. Most of the scripts will take some parameters as input (e.g. create user <x>), and this is where Ansible and Groovy will help. Both coming from the ages of REST things, they can speak and understand JSON fluently.

On the Groovy script side :

import groovy.json.JsonSlurper
parsed_args = new JsonSlurper().parseText(args)
security.setAnonymousAccess(Boolean.valueOf(parsed_args.anonymous_access))

And to call this script from Ansible passing arguments:

  - include: call_script.yml
    vars:
      script_name: setup_anonymous_access
      args: # this structure will be parsed by the groovy JsonSlurper above
        anonymous_access: true

with call_script.yml:

  ---
  - name: Calling Groovy script {{ script_name }}
    uri:
      url: "http://localhost:8081/service/siesta/rest/v1/script/{{ script_name }}/run"
      user: 'admin'
      password: "{{ current_nexus_admin_password }}"
      headers:
        Content-Type: "text/plain"
      method: POST
      status_code: 200,204
      force_basic_auth: yes
      body: "{{ args | to_json }}"

This allows us to cleanly pass structured parameters from Ansible to the Groovy scripts, keeping the objects’ structure, arrays and basic types.

Nexus Groovy Scripts Development Tips and Tricks

Here are some hints that can help a developer while working on the Groovy scripts.

Have a Classpath Setup in Your IDE

As described in the Nexus documentation, having Nexus scripting in your IDE’s classpath can really help you work. If you automate the Nexus setup as much as possible, you will inevitably stumble against some undocumented internal APIs. Additionally, some parts of the API do not have any source available (e.g. LDAP). In such cases, a decompiler can be useful.

Since our role on Github uses Maven with the all the necessary dependencies, you can simply open it with IntelliJ and edit the scripts in files/groovy.

Scripting API Entry Points

As documented, there are four implicit entry points to access Nexus internals from your script:

• core
• repository
• blobStore
• security

Those are useful for simple operations, but for anything more complicated you will need to resolve services more in-depth:

• through indirection from the main entry points: blobStore.getBlobStoreManager()
• directly by resolving an inner @Singleton from container context: container.lookup(DefaultCapabilityRegistry.class.getName())

Take Examples from Nexus’s Source Code

Some parts of Nexus (7.4%, according to Github) are also written using Groovy, containing lots of nice code examples: CoreApiImpl.groovy .

Creating HTTP requests from the configuration web interface (AJAX requests) also provides some hints about the expected data structures or parameters or values of some settings.

Last but not least, setting up a remote debugger from your IDE to a live Nexus instance can help, since there are lots of places where a very generic data structure is used (like Map<String, Object>) and only runtime inspection can quickly tell the actual needed types.

Detailed Examples

Here are some commented examples of Groovy scripts taken from the Ansible role

Setting up a Capability

Capabilities are features of Nexus that can be configured using a unified user interface. In our case, this covers:

1. anonymous access
2. base public URL
3. branding (custom HTML header/footer).

Instructions:

    import groovy.json.JsonSlurper
    import org.sonatype.nexus.capability.CapabilityReference
    import org.sonatype.nexus.capability.CapabilityType
    import org.sonatype.nexus.internal.capability.DefaultCapabilityReference
    import org.sonatype.nexus.internal.capability.DefaultCapabilityRegistry

    // unmarshall the parameters as JSON
    parsed_args = new JsonSlurper().parseText(args)

    // Type casts, JSON serialization insists on keeping those as 'boolean'
    parsed_args.capability_properties['headerEnabled'] = parsed_args.capability_properties['headerEnabled'].toString()
    parsed_args.capability_properties['footerEnabled'] = parsed_args.capability_properties['footerEnabled'].toString()

    // Resolve a @Singleton from the container context
    def capabilityRegistry = container.lookup(DefaultCapabilityRegistry.class.getName())
    def capabilityType = CapabilityType.capabilityType(parsed_args.capability_typeId)

    // Try to find an existing capability to update it
    DefaultCapabilityReference existing = capabilityRegistry.all.find {
        CapabilityReference capabilityReference ->
            capabilityReference.context().descriptor().type() == capabilityType
    }

    // update
    if (existing) {
        log.info(parsed_args.typeId + ' capability updated to: {}',
                capabilityRegistry.update(existing.id(), existing.active, existing.notes(), parsed_args.capability_properties).toString()
        )
    } else { // or create
        log.info(parsed_args.typeId + ' capability created as: {}', capabilityRegistry.
                add(capabilityType, true, 'configured through api', parsed_args.capability_properties).toString()
        )
    }

Setting up a Maven Repository Proxy

    import groovy.json.JsonSlurper
    import org.sonatype.nexus.repository.config.Configuration

    // unmarshall the parameters as JSON
    parsed_args = new JsonSlurper().parseText(args)

    // The two following data structures are good examples of things to look for via runtime inspection
    // either in client Ajax calls or breakpoints in a live server

    authentication = parsed_args.remote_username == null ? null : [
            type: 'username',
            username: parsed_args.remote_username,
            password: parsed_args.remote_password
    ]

    configuration = new Configuration(
            repositoryName: parsed_args.name,
            recipeName: 'maven2-proxy',
            online: true,
            attributes: [
                    maven  : [
                            versionPolicy: parsed_args.version_policy.toUpperCase(),
                            layoutPolicy : parsed_args.layout_policy.toUpperCase()
                    ],
                    proxy  : [
                            remoteUrl: parsed_args.remote_url,
                            contentMaxAge: 1440.0,
                            metadataMaxAge: 1440.0
                    ],
                    httpclient: [
                            blocked: false,
                            autoBlock: true,
                            authentication: authentication,
                            connection: [
                                    useTrustStore: false
                            ]
                    ],
                    storage: [
                            blobStoreName: parsed_args.blob_store,
                            strictContentTypeValidation: Boolean.valueOf(parsed_args.strict_content_validation)
                    ],
                    negativeCache: [
                            enabled: true,
                            timeToLive: 1440.0
                    ]
            ]
    )

    // try to find an existing repository to update
    def existingRepository = repository.getRepositoryManager().get(parsed_args.name)

    if (existingRepository != null) {
        // repositories need to be stopped before any configuration change
        existingRepository.stop()

        // the blobStore part cannot be updated, so we keep the existing value
        configuration.attributes['storage']['blobStoreName'] = existingRepository.configuration.attributes['storage']['blobStoreName']
        existingRepository.update(configuration)

        // re-enable the repo
        existingRepository.start()
    } else {
        repository.getRepositoryManager().create(configuration)
    }

Setting up a Role

    import groovy.json.JsonSlurper
    import org.sonatype.nexus.security.user.UserManager
    import org.sonatype.nexus.security.role.NoSuchRoleException

    // unmarshall the parameters as JSON
    parsed_args = new JsonSlurper().parseText(args)

    // some indirect way to retrieve the service we need
    authManager = security.getSecuritySystem().getAuthorizationManager(UserManager.DEFAULT_SOURCE)

    // Try to locate an existing role to update
    def existingRole = null

    try {
        existingRole = authManager.getRole(parsed_args.id)
    } catch (NoSuchRoleException ignored) {
        // could not find role
    }

    // Collection-type cast in groovy, here from String[] to Set<String>
    privileges = (parsed_args.privileges == null ? new HashSet() : parsed_args.privileges.toSet())
    roles = (parsed_args.roles == null ? new HashSet() : parsed_args.roles.toSet())

    if (existingRole != null) {
        existingRole.setName(parsed_args.name)
        existingRole.setDescription(parsed_args.description)
        existingRole.setPrivileges(privileges)
        existingRole.setRoles(roles)
        authManager.updateRole(existingRole)
    } else {
        // Another collection-type cast, from Set<String> to List<String>
        security.addRole(parsed_args.id, parsed_args.name, parsed_args.description, privileges.toList(), roles.toList())
    }

The resulting role is available at Ansible Galaxy and on Github. It features the setup of :

• Downloading and unpacking of Nexus
• SystemD service unit
• (optional) SSL-enabled apache reverse proxy
• Admin password
• LDAP
• Privileges and roles
• Local users
• Blobstores
• All types of repos
• Base URL
• Branding (custom HTML header & footer)
• Automated jobs