How to make sure docker's time syncs with that of the host?

The source for this answer is the comment to the answer at: Will docker container auto sync time with the host machine?

After looking at the answer, I realized that there is no way a clock drift will occur on the docker container. Docker uses the same clock as the host and the docker cannot change it. It means that doing an ntpdate inside the docker does not work.

The correct thing to do is to update the host time using ntpdate

As far as syncing timezones is concerned, -v /etc/localtime:/etc/localtime:ro works.

You can add your local files (/etc/timezone and /etc/localtime) as volume in your Docker container.

Update your docker-compose.yml with the following lines.

volumes:
    - "/etc/timezone:/etc/timezone:ro"
    - "/etc/localtime:/etc/localtime:ro"

Now the container time is the same as on your host.

If you are using boot2docker and ntp doesn't work inside the docker VM (you are behind a proxy which does not forward ntp packets) but your host is time-synced, you can run the following from your host:

docker-machine ssh default "sudo date -u $(date -u +%m%d%H%M%Y)"

This way you are sending your machine's current time (in UTC timezone) as a string to set the docker VM time using date (again in UTC timezone).

NOTE: in Windows, inside a bash shell (from the msys git), use:

docker-machine.exe ssh default "sudo date -u $(date -u +%m%d%H%M%Y)"