Representational State Transfer (REST) APIs are all the rage. REST was defined by Roy Thomas Fielding in his PhD dissertation “Architectural Styles and the Design of Network-based Software Architectures“. The architectural style of REST describes six constraints:

• Uniform interface
• Stateless
• Cacheable
• Client – Server communication
• Layered system
• Code on demand

RESTful APIs typically use HTTP and HTTP verbs (GET, POST, PUT, DELETE, etc.) to send data to, or retrieve data from remote systems. To do so, REST APIs use Uniform Resource Identifiers (URIs) to interact with remote systems. Thus, a client can interact with a remote system over a REST API using standard HTTP URIs and HTTP verbs. For the data transfer, common internet media types, like JSON or XML are used. It’s important to understand that REST is not a standard per se. But most implementations make use of standards such as HTTP, URI, JSON or XML.

Because of the uniform interface, you have different choices in view of a client. I will use PowerShell and the Invoke-RestMethod cmdlet in my examples.

HPE StoreVirtual REST API

With the release of LeftHand OS 11.5 (the latest release is 12.6), HPE added a REST API for management and storage provisioning. Due to a re-engineered management stack, the REST API is significantly faster than the same task processed on the CLI or using the  Centralized Management Console (CMC). It’s perfect for automation and scripting. It allows customers to achieve a higher level of automation and operational simplicity. The StoreVirtual REST API is using JavaScript Object Notation (JSON) for data transfer between client and the StoreVirtual management group. With the REST API, you can

• Read, create, and modify volumes
• Create and delete snapshots
• Create, modify, and delete servers
• Grant and revoke access of servers to volumes

I use two StoreVirtal VSA (LeftHand OS 12.6) in my lab. Everything I show in this blog post is based on LeftHand OS 12.6.

The REST API in LeftHand OS 12.6 uses:

• HTTPS 1.1
• media types application/JSON
• Internet media types application/schema+JSON
• UTF-8 character encoding

RESTful APIs typically use HTTP and HTTP verbs (GET, POST, PUT, DELETE, etc.). I case of the StoreVirtual REST API:

• GET is used to retrieve an object. No body is necessary.
• PUT is used to update an object. The information to update the object is sent within the body.
• POST is used to create of an object, or to invoke an action or event. The necessary information are sent within the body.
• DELETE is used to delete an object.

Entry point for all REST API calls is /lhos, starting from a node, eg.

https://fqdn-or-ip:8081/lhos/

Subsequent resources are relative to this base URI. Resources are:

The object model of the StoreVirtual REST API uses

• Collections, and
• Entities

to address resources. An entity is used to address individual resources, whereas a collection is a group of individual resources. Resources can be addressed by using a URI.

Exploring the API

First of all, we need to authenticate us. Without a valid authentication token, no REST API queries can be made. To create a credential entity, we have to use the POST method.

$cred = @{
            user='admin';
            password='Passw0rd'
}

$body = $cred | ConvertTo-Json

$a = Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/credentials -Method Post -Body $body -ContentType 'application/JSON'

$cred is a hash table which includes the username and the password. This hash table is converted to the JSON format with the ConvertTo-Json cmdlet. The JSON data will be used as body for our query. The result is an authentication token.

PS C:\Users\p.terlisten> $a

authToken                                                                                                                                                                                     
---------                                                                                                                                                                                     
fa0a7b56-0134-400f-9d62-79b3071c950a

This authentication token must be used for all subsequent API queries. This query retrieves a collection of all valid sessions.

$b = Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/credentials -Method Get -Headers @{'Authorization'=$a.authToken}

The GET method is used, and the authentication token is sent with the header of the request.

PS C:\Users\p.terlisten> $b


name        : REST Sessions Collection
description : Collection of authentication sessions used by the REST server.
type        : RESTSession
uri         : /lhos/credentials
total       : 1
members     : {@{name=fa0a7b56-0134-400f-9d62-79b3071c950a; description=REST Session; type=RESTSession; id=0; uri=/lhos/credentials/fa0a7b56-0134-400f-9d62-79b3071c950a; 
              created=2016-06-07T08:38:06.426241Z; modified=2016-06-07T08:44:28.255283Z; userName=admin; clientIP=192.168.200.90}}

To retrieve an individual credential entity, the URI of the entity must be used.

$b = Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/credentials/fa0a7b56-0134-400f-9d62-79b3071c950a -Method Get -Headers @{'Authorization'=$a.authToken}

The result of this query is the individual credential entity

PS C:\Users\p.terlisten> $b


name        : fa0a7b56-0134-400f-9d62-79b3071c950a
description : REST Session
type        : RESTSession
id          : 0
uri         : /lhos/credentials/fa0a7b56-0134-400f-9d62-79b3071c950a
created     : 2016-06-07T08:38:06.426241Z
modified    : 2016-06-07T08:51:56.358096Z
userName    : admin
clientIP    : 192.168.200.90

It’s important to know, that if a session has not been used for 15 minutes, it is automatically removed. The same applies to constantly active sessions after 24 hours. After 24 hours, the credential entity will be automatically removed.

Let’s try to create a volume. The information about this new volume has to be sent within the body of our request. We use again the ConvertTo-Json cmdlet to convert a hash table with the necessary information to the JSON format.

$vol = @{
            name='api-vol';
            description='Volume created via REST API';
            size=1073741824;
            clusterId=28;
            isThinProvisioned=$true;
            dataProtectionLevel=2
}

$body = $vol | ConvertTo-Json

Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/volumes -Method Post -Headers @{'Authorization'=$a.authToken} -Body $body -ContentType 'application/JSON'

The size must be specified in bytes. As a result, Invoke-RestMethod will output this:

name                          : api-vol
description                   : Volume created via REST API
type                          : volume
id                            : 3058
uri                           : /lhos/volumes/3058
created                       : 2016-06-07T08:55:41Z
modified                      : 
friendlyName                  : 
transport                     : 0
isThinProvisioned             : True
size                          : 1073741824
serialNumber                  : f9df3e8bb0a160f269027ecc0371884e0000000000000bf2
provisionedSpace              : 1073741824
numberOfReplicas              : 2
dataProtectionLevel           : 2
iscsiIqn                      : iqn.2003-10.com.lefthandnetworks:mgmt:3058:api-vol
isPrimary                     : True
isDeleting                    : False
bytesWritten                  : 0
isAvailable                   : True
clusterName                   : CLUSTER
clusterId                     : 28
isVIPRebalancing              : False
isAdaptiveOptimizationEnabled : True
isMigrating                   : False
scsiLUNStatus                 : available
hasUnrecoverableIOErrors      : False
restripePendingStatus         : none
replicationStatus             : normal
resynchronizationStatus       : none
migrationStatus               : none
isLicensed                    : True
transportServerId             : 0
fcTransportStatus             : 0
createdBy                     : Unknown
iscsiSessions                 : 
fibreChannelPaths             : 
snapshots                     : @{name=snapshots; type=snapshot; uri=/snapshots?volumeName=api-vol; resource=}

Using the CMC, we can confirm that the volume was successfully created.

Patrick Terlisten/ www.vcloudnine.de/ Creative Commons CC0

Since we have a volume, we can create a snapshot. To create a snapshot, we need to invoke an action on the volume entity. We have to use the POST method and the URI of our newly created volume.

$snapshot = @{
                action='createSnapshot';
                parameters = @{
                                name='vol-api-snap';
                                description='Volume snapshot created via REST API';
}
}

$body = $snapshot | ConvertTo-Json

Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/volumes/3058 -Method Post -Headers @{'Authorization'=$a.authToken} -Body $body -ContentType 'application/JSON'

In case of a successful query, Invoke-RestMethod will give us this output.

name                     : vol-api-snap
description              : Volume snapshot created via REST API
type                     : snapshot
id                       : 3060
uri                      : /lhos/snapshots/3060
created                  : 2016-06-07T09:01:12Z
modified                 : 
friendlyName             : 
transport                : 0
isThinProvisioned        : True
size                     : 1073741824
serialNumber             : f9df3e8bb0a160f269027ecc0371884e0000000000000bf4
provisionedSpace         : 8388608
iscsiIqn                 : iqn.2003-10.com.lefthandnetworks:mgmt:3060:vol-api-snap
isPrimary                : True
isDeleting               : False
bytesWritten             : 0
isAvailable              : True
clusterName              : CLUSTER
clusterId                : 28
iscsiSessions            : 
fibreChannelPaths        : 
snapshotACL              : 
writableSpaceUsed        : 0
managedBy                : 0
isAutomatic              : False
isMigrating              : False
scsiLUNStatus            : available
hasUnrecoverableIOErrors : False
restripePendingStatus    : none
replicationStatus        : normal
resynchronizationStatus  : none
migrationStatus          : none
isLicensed               : True
transportServerId        : 0
fcTransportStatus        : 0
createdBy                : Unknown

Again, we can use the CMC to confirm the success of our operation.

Patrick Terlisten/ www.vcloudnine.de/ Creative Commons CC0

To delete the snapshot, the DELETE method and the URI of the snapshot entity must be used.

Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/snapshots/3060 -Method Delete -Headers @{'Authorization'=$a.authToken}

To confirm the successful deletion of the snapshot, the GET method can be used. The GET method will retrieve a collection of all snapshot entities.

Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/snapshots -Method Get -Headers @{'Authorization'=$a.authToken}

The result will show no members inside of the snapshot collection.

name        : Snapshots Collection
description : Collection of Snapshot objects
type        : snapshot
uri         : /lhos/snapshots
total       : 0
members     : {}

At the end of the day, we remove our credential entity, because it’s not longer used. To delete the credential entity, we use the DELETE method with the URI of our credential entity.

Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/credentials/fa0a7b56-0134-400f-9d62-79b3071c950a -Method Delete -Headers @{'Authorization'=$a.authToken}

The next query should fail, because the credential entity is no longer valid.

PS C:\Users\p.terlisten> Invoke-RestMethod -Uri https://vsa1.lab.local:8081/lhos/credentials -Method Get -Headers @{'Authorization'=$a.authToken}
The remote server returned an error: (401) Unauthorized. (raised by: Invoke-RestMethod)

HTTPS workaround

The StoreVirtual API is only accessable over HTTPS. By default, the StoreVirtual nodes use an untrusted HTTPS certifificate. This will cause Invoke-RestMethod to fail.

[10,6: Invoke-RestMethod] The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

After a little research, I found a workaround. This workaround uses the System.Security.Cryptography.X509Certificates namespace. You can use this snippet to build a function or add it to a try-catch block.

add-type @"
    using System.Net;
    using System.Security.Cryptography.X509Certificates;
    public class TrustAllCertsPolicy : ICertificatePolicy {
        public bool CheckValidationResult(
            ServicePoint srvPoint, X509Certificate certificate,
            WebRequest request, int certificateProblem) {
            return true;
        }
    }
"@

[System.Net.ServicePointManager]::CertificatePolicy = New-Object TrustAllCertsPolicy

Final words

The StoreVirtual REST API is really handy. It can be used to perform all important tasks. It’s perfect for automation and it’s faster than the CLI. I’ve used PowerShell in my examples, but I’ve successfully tested it with Python. Make sure to take a look in to the HPE StoreVirtual REST API Reference Guide.