Use Swiftly to download an exported image

  • Last updated on: 2018-04-09
  • Authored by: Cloud Images

This article describes two ways in which you can use the Swiftly client to download from Cloud Files an image that you have exported from Cloud Images. It presumes that you have already used a Cloud Images export task to export one of your images from the Rackspace open cloud, that you understand how exported images are stored in Cloud Files as Dynamic Large Objects (DLOs), and that you have installed the Swiftly client for Cloud Files. If you need help with any of these topics, see the following sources:

Download your entire image at once

To download your entire image at once, perform the following tasks.

Set the environment variables

In a bash shell, set the following environment variables:

CF_USERNAME=      # your Rackspace cloud username
CF_API_KEY=       # your Rackspace cloud API key
CF_REGION=        # the 3-character region code for the location associated with your exported image (for example, ORD)
LOCALFILENAME=    # what you want to name the downloaded image file
CONTAINER=        # the container in Cloud Files that contains your exported image
IMAGEFILENAME=    # the name of your exported image in Cloud Files

For information about viewing your Rackspace API key, see View and reset your API key.

Invoke Swiftly

After you set the environment variables, invoke Swiftly from the command line to perform the download, as follows.

Note: Consider using a screen session to perform this task. If you’re not familiar with the GNU Screen program, you can find an introduction in Install the Swiftly client for Cloud Files.

swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  get
    --output=${LOCALFILENAME}
  ${CONTAINER}/${IMAGEFILENAME}

If you’re downloading to a cloud server that’s already in the Rackspace open cloud, add the --snet option to the command so that the file is transferred over the internal cloud network. Additionally, if you want Swiftly to notify you about what is occurring while your image file is downloading, you can add the --verbose option. The following example shows how to include these options:

swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  --snet
  --verbose
  get
    --output=${LOCALFILENAME}
  ${CONTAINER}/${IMAGEFILENAME}

The following code block shows the verbose response for the preceding call. (This image is a little over 2 GB.)

VERBOSE 0.00 1 Attempting auth v2 RAX-KSKEY:apiKeyCredentials with https://identity.api.rackspacecloud.com/v2.0
VERBOSE 0.00 1 Establishing HTTPS connection to identity.api.rackspacecloud.com
VERBOSE 0.00 1 > POST /v2.0/tokens
VERBOSE 0.00 1 > {"auth": {"RAX-KSKEY:apiKeyCredentials": {"username": "joeuser", "apiKey": "968f8053a6f34677b70a3787cd3bd18a"}}}
VERBOSE 0.55 1 < 200 OK
VERBOSE 0.55 1 Establishing HTTPS connection to snet-storage101.iad3.clouddrive.com
VERBOSE 0.57 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 0.93 1 < 200 OK

Check the download

The time that it takes for Swiftly to complete the download depends on the speed of your network connection and general network congestion. In some cases, the download might complete prematurely. To verify that this hasn’t occurred, compare the size in bytes of the file that you receive with the size of the file that exists in Cloud Files. If they’re not the same size, a problem has occurred.

To determine the size of the file that you received, check your local file system:

$ ls -l
total 2524008
-rw-rw-r-- 1 joeuser joeuser 2584576512 Apr 28 19:52 downloaded-image.vhd

You can use Swiftly to determine the size of the file in Cloud Files:

swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  head
  ${CONTAINER}/${IMAGEFILENAME}

The response should be similar to the following one. The file size is the value in the Content-Length header.

Content-Length:    2584576512
Content-Type:      application/octet-stream
Etag:              "83dce2d37b7046228f72c1e5c688d8c8"
Last-Modified:     Fri, 28 Feb 2014 21:37:36 GMT
X-Object-Manifest: exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-
X-Timestamp:       1393623455.54221
X-Trans-Id:        txe67683c4407d4e8aa01b8-00535eac8aiad3

In the preceding examples, the size of the local file in bytes matches the Content-Length of the Dynamic Large Object (DLO) in Cloud Files. Therefore, the download did not end prematurely. However, this information only indicates that the correct number of bytes was received. It does not tell you that the value of every byte is correct.

If you suspect that your download was corrupted, or if you’re trying to download an image from data centers one side of the world to the other, you might want to try the alternative method that is described in the next section.

Alternative download method

If your image is very large or if you experience network interruptions, the download method outlined in the preceding section might fail repeatedly. This section describes an alternative method that involves downloading the individual segments that comprise the object. This method has the following advantages:

  • This method works with smaller, more manageable pieces.
  • You can verify the checksum for each of the pieces to ensure that no part is corrupted.
  • If a segment is faulty, you need to re-download only the faulty segment.
  • After you have all of the pieces, you can stream them locally into a single Virtual Hard Disk (VHD) file.

Note: This section assumes that you have set all of the environment variables described in the preceding section.

Get the DLO manifest

Use the following command to get the DLO manifest:

swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  head
  ${CONTAINER}/${IMAGEFILENAME}

The response will be similar to the following one:

Content-Length:    2584576512
Content-Type:      application/octet-stream
Etag:              "83dce2d37b7046228f72c1e5c688d8c8"
Last-Modified:     Fri, 28 Feb 2014 21:37:36 GMT
X-Object-Manifest: exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-
X-Timestamp:       1393623455.54221
X-Trans-Id:        tx020fee01f492491abc2ac-00535d40f7iad3

The X-Object-Manifest header indicates that this is a DLO. The value of this header specifies the container where the segments are located (in this example, exports) and the pattern that is used to find the segments in that container (in this example, 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-). When you request a download of this manifest object, Cloud Files accesses the container in your account that is named exports, finds all of the objects in it that have names that match the pattern 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-, and streams them out in alphabetical order.

Get the detailed list of segments

Note: Before reading this section, you might want to review Where is my exported image? in the Cloud Images FAQ for a reminder of the naming conventions used by Cloud Images export task.

Now that you know the container and pattern that will be used to locate the segments for the DLO that you want to download, you can use Swiftly to get a detailed list of the segments:

CONTAINER="exports"
PATTERN="9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-"
swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  get
    --prefix=${PATTERN}
    --full
  ${CONTAINER}

The following code block shows a sample response:

   1048576000 2014-02-28 21:33:46.41 699580384e28b7c2b3b8d916169c11ca  application/octet-stream 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001
   1048576000 2014-02-28 21:35:43.81 b513404695fc1117c42ee6dc7de91ef1  application/octet-stream 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002
    487424512 2014-02-28 21:36:55.05 372d9904e2048dc84dea82fdb0ead10e  application/octet-stream 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003

The output provides the following information:

   number-of-bytes   creation-date-time   MD5-checksum   output-type   segment-name

In this example, the DLO has three segments. The first two are the same size and the final segment is smaller.

Download the segments

You can use Swiftly to download the individual segments to a local directory. Ensure that this directory already exists in your file system before attempting the download.

LOCAL_DIR="my-images"
swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  --verbose
  get
    --prefix=${PATTERN}
    --all-objects
    --output=${LOCAL_DIR}/
  ${CONTAINER}

The following code shows sample output when the Swiftly --verbose option is used:

VERBOSE 0.00 1 Attempting auth v2 RAX-KSKEY:apiKeyCredentials with https://identity.api.rackspacecloud.com/v2.0
VERBOSE 0.00 1 Establishing HTTPS connection to identity.api.rackspacecloud.com
VERBOSE 0.00 1 > POST /v2.0/tokens
VERBOSE 0.00 1 > {"auth": {"RAX-KSKEY:apiKeyCredentials": {"username": "joeuser", "apiKey": "968f8053a6f34677b70a3787cd3bd18a"}}}
VERBOSE 0.34 1 < 200 OK
VERBOSE 0.34 1 Establishing HTTPS connection to storage101.iad3.clouddrive.com
VERBOSE 0.36 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports?format=json&prefix=9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd- User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 0.37 1 < 200 OK
VERBOSE 0.38 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001 User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 0.48 1 < 200 OK
VERBOSE 14.53 1 Establishing HTTPS connection to storage101.iad3.clouddrive.com
VERBOSE 14.54 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002 User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 14.61 1 < 200 OK
VERBOSE 207.58 1 Establishing HTTPS connection to storage101.iad3.clouddrive.com
VERBOSE 207.59 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003 User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 207.76 1 < 200 OK
VERBOSE 218.22 1 Establishing HTTPS connection to storage101.iad3.clouddrive.com
VERBOSE 218.23 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports?format=json&marker=9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003&prefix=9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd- User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 218.24 1 < 200 OK

In this example, the following segments were downloaded:

$ ls -l my-images/
total 1853964
-rw-rw-r-- 1 joeuser joeuser 1048576000 Feb 28 21:33 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001
-rw-rw-r-- 1 joeuser joeuser  362443328 Feb 28 21:35 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002
-rw-rw-r-- 1 joeuser joeuser  487424512 Feb 28 21:36 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003

Recall from Where is my exported image? in the Cloud Images FAQ that each segment should be the same size except for the final segment, which can be smaller. Therefore, segment-00002 should be the same size as segment-00001, and it is not. This information indicates that segment-00002 is corrupted.

The next step determines if the final segment is the correct size. Earlier, you invoked Swiftly with the --full option to get the full details on all of the segments in the exports container that match the pattern 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-. From that sample output, you see that the final segment should be 487424512 bytes, and segment-00003 matches that value.

Download a segment (if necessary)

If you need to download a fresh copy of a bad segment, use the following commands:

SEGMENT_NAME="9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002"
swiftly
  --auth-url=https://identity.api.rackspacecloud.com/v2.0
  --auth-user=$CF_USERNAME
  --auth-key=$CF_API_KEY
  --region=$CF_REGION
  --verbose
  get
    --output=${LOCAL_DIR}/${SEGMENT_NAME}
  ${CONTAINER}/${SEGMENT_NAME}

The verbose output will be similar to the following sample output:

VERBOSE 0.01 1 Attempting auth v2 RAX-KSKEY:apiKeyCredentials with https://identity.api.rackspacecloud.com/v2.0
VERBOSE 0.01 1 Establishing HTTPS connection to identity.api.rackspacecloud.com
VERBOSE 0.01 1 > POST /v2.0/tokens
VERBOSE 0.01 1 > {"auth": {"RAX-KSKEY:apiKeyCredentials": {"username": "joeuser", "apiKey": "968f8053a6f34677b70a3787cd3bd18a"}}}
VERBOSE 0.38 1 < 200 OK
VERBOSE 0.38 1 Establishing HTTPS connection to storage101.iad3.clouddrive.com
VERBOSE 0.39 1 > GET /v1/MossoCloudFS_d4fef4ad-71f1-4ec4-b5fa-f15bf3317d0d/exports/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002 User-Agent: Swiftly v2.02  X-Auth-Token: 5c2ddf4d5031452fb2bae430560aa592
VERBOSE 0.47 1 < 200 OK

Now, view the segments that have been downloaded:

$ ls -l my-images
total 2524016
-rw-rw-r-- 1 joeuser joeuser 1048576000 Feb 28 21:33 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001
-rw-rw-r-- 1 joeuser joeuser 1048576000 Apr 29 02:59 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002
-rw-rw-r-- 1 joeuser joeuser  487424512 Feb 28 21:36 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003

The second segment has the correct size.

Verify the MD5 checksums

All of the segments have the correct size. However, you must also verify that the content of each segment is correct. To verify that the content is correct, get the MD5 checksum of each segment and compare it to the MD5 checksum of the corresponding segment in Cloud Files. (The list of MD5 checksums of the segments in Cloud Files were displayed when you invoked Swiftly with the --full option above to get the detailed list of segments.)

$ cd my-images

$ for i in $(ls -1 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-*); do md5sum $i ; done
699580384e28b7c2b3b8d916169c11ca  9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001
b513404695fc1117c42ee6dc7de91ef1  9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002
372d9904e2048dc84dea82fdb0ead10e  9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003

In the output from the md5sum command, the checksum is on the left and the file name is on the right. If you compare the checksums that are displayed here with the ones that you got from Cloud Files earlier, you can see that they match. This match indicates that the segments have downloaded successfully.

Reconstitute the VHD file

After all of the segments have been downloaded correctly, you can create a single VHD file:

# still in the "my-images" directory
$ cat 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-0000* > 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd

# let's see what we've got now
$ ls -l
total 5048020
-rw-rw-r-- 1 joeuser joeuser 2584576512 Apr 29 03:20 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd
-rw-rw-r-- 1 joeuser joeuser 1048576000 Feb 28 21:33 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001
-rw-rw-r-- 1 joeuser joeuser 1048576000 Apr 29 02:59 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002
-rw-rw-r-- 1 joeuser joeuser  487424512 Feb 28 21:36 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003

Earlier in this article, we used Swiftly to perform a HEAD request on the DLO in Cloud Files and determined that the Content-Length for a request of the DLO is 2584576512 bytes. That is the size of the reconstituted VHD file.

While you could compute an MD5 checksum of the VHD file, there is nothing to compare it to. Because a DLO isn’t a real object in Cloud Files (but is a series of segment objects whose content is streamed out in a particular order), Cloud Files doesn’t store an MD5 checksum for the object. In addition, the checksum is unnecessary because the VHD file is made up of three segments, each segment has the correct content, and the segments have been put together in the correct order. Therefore, the VHD file must be identical to the file that was exported from Cloud Images into Cloud Files.

Clean up your file system

After you download your image, you might want to clean up your file system. Your directory might be similar to the one in the following example:

ls -lh my-images
total 4.9G
-rw-rw-r-- 1 joeuser joeuser  2.5G Apr 29 03:20 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd
-rw-rw-r-- 1 joeuser joeuser 1000M Feb 28 21:33 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00001
-rw-rw-r-- 1 joeuser joeuser 1000M Apr 29 02:59 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00002
-rw-rw-r-- 1 joeuser joeuser  465M Feb 28 21:36 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-00003

Unlike in Cloud Files, where the segments contain data and the DLO is simply a manifest telling Cloud Files what the content of the DLO is, these are all real files. You can see that this is the case by asking the operating system to display the amount of space that these files take up:

$ du -chs my-images
4.9G    my-images
4.9G    total

Note that twice as much space as the size of the VHD file is used. Because you’ve used the segments to reconstitute the VHD file, you no longer need the segments locally. You can delete them without affecting the VHD file in the following way:

$ rm my-images/9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd-0000*

$ ls -lh my-images
total 2.5G
-rw-rw-r-- 1 joeuser joeuser 2.5G Apr 29 03:20 9af8acc8-8189-48b9-b3d6-8152c60074d8.vhd

$ du -chs my-images
2.5G    my-images
2.5G    total

The 2.5 GB VHD file remains.

Warning: Remember that in Cloud Files, DLOs have a different relationship with their segments. If you delete segments in Cloud Files, you corrupt your DLO and your VHD file.

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