My suggestion: The UI has a notification at the top alerting the user there is a new update and they should reboot the moblab.

This way if they are running the SSD test (3 weeks) they can get the update after the test is finished.

Is there an api/command to know if there is an update downloaded on the system? 

+Deymo

update_engine_client should help here.

From the --help output:
  --is_reboot_needed  (Exit status 0 if reboot is needed, 2 if reboot is not needed or 1 if an error occurred.)  type: bool  default: false

You can also make it block until the reboot is needed.

while ! update_engine_client --block_until_reboot_is_needed; do
  sleep 1; # Something went wrong talking to update_engine
done
reboot

sounds like a good idea to go.

Prioritizing it for M-56

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/d3a3c24b3f014272c5e661bd6b7871040ebdd22e

commit d3a3c24b3f014272c5e661bd6b7871040ebdd22e
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Jan 26 21:25:39 2018

[moblab] give apache permission to call update_engine_client

BUG= chromium:613747 
TEST=local moblab device

Change-Id: Iec72cfa80b9c4efcbcc01691925c404aaa96d237
Reviewed-on: https://chromium-review.googlesource.com/887732
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>

[rename] https://crrev.com/d3a3c24b3f014272c5e661bd6b7871040ebdd22e/project-moblab/chromeos-base/chromeos-bsp-moblab/chromeos-bsp-moblab-0.0.5-r79.ebuild
[modify] https://crrev.com/d3a3c24b3f014272c5e661bd6b7871040ebdd22e/project-moblab/chromeos-base/chromeos-bsp-moblab/chromeos-bsp-moblab-0.0.5.ebuild

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/b0f8dc76b36d2b04e08024e98add237597e59d35

commit b0f8dc76b36d2b04e08024e98add237597e59d35
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Jan 26 21:51:13 2018

[moblab] Add update button

BUG= chromium:613747 
TEST=Tested features on a local moblab

Change-Id: Id512a96e57c5449ace561b8a551b2570ab637468
Reviewed-on: https://chromium-review.googlesource.com/887794
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>

[modify] https://crrev.com/b0f8dc76b36d2b04e08024e98add237597e59d35/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java
[modify] https://crrev.com/b0f8dc76b36d2b04e08024e98add237597e59d35/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/b0f8dc76b36d2b04e08024e98add237597e59d35/frontend/client/src/autotest/moblab/rpc/VersionInfo.java
[modify] https://crrev.com/b0f8dc76b36d2b04e08024e98add237597e59d35/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/b0f8dc76b36d2b04e08024e98add237597e59d35/frontend/client/src/autotest/moblab/rpc/MoblabRpcHelper.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5

commit ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Jan 26 22:46:44 2018

[moblab] Add update button

BUG= chromium:613747 
TEST=Tested features on a local moblab

Change-Id: Id512a96e57c5449ace561b8a551b2570ab637468
Reviewed-on: https://chromium-review.googlesource.com/887794
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit b0f8dc76b36d2b04e08024e98add237597e59d35)
Reviewed-on: https://chromium-review.googlesource.com/890098
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[modify] https://crrev.com/ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java
[modify] https://crrev.com/ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5/frontend/client/src/autotest/moblab/rpc/VersionInfo.java
[modify] https://crrev.com/ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/ed5ed01485afa6f55dc8c0a5793dc73620cbb7f5/frontend/client/src/autotest/moblab/rpc/MoblabRpcHelper.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/872b9e2e4ac95220b716de09c5cb09e83a162b8d

commit 872b9e2e4ac95220b716de09c5cb09e83a162b8d
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Jan 26 22:46:45 2018

[moblab] give apache permission to call update_engine_client

BUG= chromium:613747 
TEST=local moblab device

Change-Id: Iec72cfa80b9c4efcbcc01691925c404aaa96d237
Reviewed-on: https://chromium-review.googlesource.com/887732
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit d3a3c24b3f014272c5e661bd6b7871040ebdd22e)
Reviewed-on: https://chromium-review.googlesource.com/889688
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[add] https://crrev.com/872b9e2e4ac95220b716de09c5cb09e83a162b8d/project-moblab/chromeos-base/chromeos-bsp-moblab/chromeos-bsp-moblab-0.0.5-r79.ebuild
[modify] https://crrev.com/872b9e2e4ac95220b716de09c5cb09e83a162b8d/project-moblab/chromeos-base/chromeos-bsp-moblab/chromeos-bsp-moblab-0.0.5.ebuild

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/400221f4efe03d00a19337f8ec2b3a3de712d1fa

commit 400221f4efe03d00a19337f8ec2b3a3de712d1fa
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Jan 26 22:46:47 2018

[moblab] give apache permission to call update_engine_client

BUG= chromium:613747 
TEST=local moblab device

Change-Id: Iec72cfa80b9c4efcbcc01691925c404aaa96d237
Reviewed-on: https://chromium-review.googlesource.com/887732
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit d3a3c24b3f014272c5e661bd6b7871040ebdd22e)
Reviewed-on: https://chromium-review.googlesource.com/889687
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[add] https://crrev.com/400221f4efe03d00a19337f8ec2b3a3de712d1fa/project-moblab/chromeos-base/chromeos-bsp-moblab/chromeos-bsp-moblab-0.0.5-r79.ebuild
[modify] https://crrev.com/400221f4efe03d00a19337f8ec2b3a3de712d1fa/project-moblab/chromeos-base/chromeos-bsp-moblab/chromeos-bsp-moblab-0.0.5.ebuild

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4

commit 5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Jan 26 22:46:47 2018

[moblab] Add update button

BUG= chromium:613747 
TEST=Tested features on a local moblab

Change-Id: Id512a96e57c5449ace561b8a551b2570ab637468
Reviewed-on: https://chromium-review.googlesource.com/887794
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit b0f8dc76b36d2b04e08024e98add237597e59d35)
Reviewed-on: https://chromium-review.googlesource.com/890078
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[modify] https://crrev.com/5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java
[modify] https://crrev.com/5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4/frontend/client/src/autotest/moblab/rpc/VersionInfo.java
[modify] https://crrev.com/5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/5f871a0f22abb4ec3c761fd8ed7db8be8fb663d4/frontend/client/src/autotest/moblab/rpc/MoblabRpcHelper.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/c223505b3ed3e90c57c5bd4fb98799c9e8fa0078

commit c223505b3ed3e90c57c5bd4fb98799c9e8fa0078
Author: Matt Mallett <mattmallett@chromium.org>
Date: Wed Jan 31 21:23:51 2018

[moblab] Use the is_reboot_needed value correctly

Use the return code from --is_reboot_needed correctly
to cause the moblab device to update when a new
version is downloaded and ready to install

BUG= chromium:613747 
TEST=updated local moblab device from 10176.62.0 to 10176.65.0 via UI

Change-Id: I2204b3fcf2a2602b72350d380d3112a47a48a2ad
Reviewed-on: https://chromium-review.googlesource.com/895905
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>

[modify] https://crrev.com/c223505b3ed3e90c57c5bd4fb98799c9e8fa0078/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/c223505b3ed3e90c57c5bd4fb98799c9e8fa0078/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/c223505b3ed3e90c57c5bd4fb98799c9e8fa0078/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/39266c967c34d0ad1530314c1f03bfe2cfa2ecb4

commit 39266c967c34d0ad1530314c1f03bfe2cfa2ecb4
Author: Matt Mallett <mattmallett@chromium.org>
Date: Thu Feb 01 00:28:12 2018

[moblab] Use the is_reboot_needed value correctly

Use the return code from --is_reboot_needed correctly
to cause the moblab device to update when a new
version is downloaded and ready to install

BUG= chromium:613747 
TEST=updated local moblab device from 10176.62.0 to 10176.65.0 via UI

Change-Id: I2204b3fcf2a2602b72350d380d3112a47a48a2ad
Reviewed-on: https://chromium-review.googlesource.com/895905
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit c223505b3ed3e90c57c5bd4fb98799c9e8fa0078)
Reviewed-on: https://chromium-review.googlesource.com/896486
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[modify] https://crrev.com/39266c967c34d0ad1530314c1f03bfe2cfa2ecb4/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/39266c967c34d0ad1530314c1f03bfe2cfa2ecb4/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/39266c967c34d0ad1530314c1f03bfe2cfa2ecb4/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/ae24cf391684582721deb92620035310d9ab4092

commit ae24cf391684582721deb92620035310d9ab4092
Author: Matt Mallett <mattmallett@chromium.org>
Date: Thu Feb 01 00:28:14 2018

[moblab] Use the is_reboot_needed value correctly

Use the return code from --is_reboot_needed correctly
to cause the moblab device to update when a new
version is downloaded and ready to install

BUG= chromium:613747 
TEST=updated local moblab device from 10176.62.0 to 10176.65.0 via UI

Change-Id: I2204b3fcf2a2602b72350d380d3112a47a48a2ad
Reviewed-on: https://chromium-review.googlesource.com/895905
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit c223505b3ed3e90c57c5bd4fb98799c9e8fa0078)
Reviewed-on: https://chromium-review.googlesource.com/896378
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[modify] https://crrev.com/ae24cf391684582721deb92620035310d9ab4092/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/ae24cf391684582721deb92620035310d9ab4092/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/ae24cf391684582721deb92620035310d9ab4092/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/b879766de2fe6fcc9beb9dc76587a20fe2c9499d

commit b879766de2fe6fcc9beb9dc76587a20fe2c9499d
Author: Matt Mallett <mattmallett@chromium.org>
Date: Fri Feb 02 20:08:13 2018

[moblab] correctly display update progress on UI

Wait for the update engine to finish checking for an update before
returning from the RPC. Also improve messaging on the UI to make
update progress easy to follow.

BUG= chromium:613747 
TEST=local moblab tested by updating from R64-10176.62.0 to
R64010176.65.0

Change-Id: I16910cc1365dc65980e269da7bbcabc28e28af43
Reviewed-on: https://chromium-review.googlesource.com/898254
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>

[modify] https://crrev.com/b879766de2fe6fcc9beb9dc76587a20fe2c9499d/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/b879766de2fe6fcc9beb9dc76587a20fe2c9499d/frontend/client/src/autotest/moblab/rpc/VersionInfo.java
[modify] https://crrev.com/b879766de2fe6fcc9beb9dc76587a20fe2c9499d/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/b879766de2fe6fcc9beb9dc76587a20fe2c9499d/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/427f50a81ba9587b947a7e3c54063207d2bbcb8c

commit 427f50a81ba9587b947a7e3c54063207d2bbcb8c
Author: Matt Mallett <mattmallett@chromium.org>
Date: Sat Feb 03 00:13:16 2018

[moblab] correctly display update progress on UI

Wait for the update engine to finish checking for an update before
returning from the RPC. Also improve messaging on the UI to make
update progress easy to follow.

BUG= chromium:613747 
TEST=local moblab tested by updating from R64-10176.62.0 to
R64010176.65.0

Change-Id: I16910cc1365dc65980e269da7bbcabc28e28af43
Reviewed-on: https://chromium-review.googlesource.com/898254
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit b879766de2fe6fcc9beb9dc76587a20fe2c9499d)
Reviewed-on: https://chromium-review.googlesource.com/900026
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[modify] https://crrev.com/427f50a81ba9587b947a7e3c54063207d2bbcb8c/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/427f50a81ba9587b947a7e3c54063207d2bbcb8c/frontend/client/src/autotest/moblab/rpc/VersionInfo.java
[modify] https://crrev.com/427f50a81ba9587b947a7e3c54063207d2bbcb8c/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/427f50a81ba9587b947a7e3c54063207d2bbcb8c/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/4955fa7407d1c9466af66e794545054ea2a4961d

commit 4955fa7407d1c9466af66e794545054ea2a4961d
Author: Matt Mallett <mattmallett@chromium.org>
Date: Sat Feb 03 00:13:19 2018

[moblab] correctly display update progress on UI

Wait for the update engine to finish checking for an update before
returning from the RPC. Also improve messaging on the UI to make
update progress easy to follow.

BUG= chromium:613747 
TEST=local moblab tested by updating from R64-10176.62.0 to
R64010176.65.0

Change-Id: I16910cc1365dc65980e269da7bbcabc28e28af43
Reviewed-on: https://chromium-review.googlesource.com/898254
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit b879766de2fe6fcc9beb9dc76587a20fe2c9499d)
Reviewed-on: https://chromium-review.googlesource.com/900025
Commit-Queue: Matt Mallett <mattmallett@chromium.org>
Trybot-Ready: Matt Mallett <mattmallett@chromium.org>

[modify] https://crrev.com/4955fa7407d1c9466af66e794545054ea2a4961d/frontend/afe/moblab_rpc_interface_unittest.py
[modify] https://crrev.com/4955fa7407d1c9466af66e794545054ea2a4961d/frontend/client/src/autotest/moblab/rpc/VersionInfo.java
[modify] https://crrev.com/4955fa7407d1c9466af66e794545054ea2a4961d/frontend/afe/moblab_rpc_interface.py
[modify] https://crrev.com/4955fa7407d1c9466af66e794545054ea2a4961d/frontend/client/src/autotest/moblab/wizard/ConfigWizard.java