Zero Downtime Deploys
New
Introduced in 0.3.0
Following a deploy, dokku will now wait 10 seconds before routing traffic to the new container. If the container is not running after this time, then the deploy is failed and your old container will continue serving traffic. You can modify this value using the following command:
If your application needs a longer period to boot up - perhaps to load data into memory, or because of slow boot time - you may also use dokku's checks functionality to more precisely check whether an application can serve traffic or not.
To specify checks, add a CHECKS file to the root of your project directory. This is a text file with one line per check. Empty lines and lines starting with # are ignored.
A check is a relative URL and may be followed by expected content from the page, for example:
Dokku will wait 5 seconds before running the checks to give the server time to start. This value can be overridden on a per-app basis in the CHECKS file by setting WAIT=nn. You may also override this for the global dokku installation:
Dokku will wait 60 seconds before stopping the old container so that existing connections are given a chance to complete. This value is also configurable globally:
Info
Note that during this time, multiple containers may be running on your server, which can be an issue for memory-hungry applications on memory-constrained servers.
Dokku will retry the checks 5 times until the checks are successful. If all 5 checks fail, the deployment is considered failed. This can be overridden in the CHECKS file by setting ATTEMPTS=nn. This number is also configurable globally:
You can also choose to skip checks completely either globally or on a per-application basis:
# globally
dokku config:set --global DOKKU_SKIP_ALL_CHECKS=true
# for APP
dokku config:set APP DOKKU_SKIP_ALL_CHECKS=true
Checks Examples
The CHECKS file may contain empty lines, comments (lines starting with #), settings (NAME=VALUE) and check instructions.
The format of a check instruction is a path, optionally followed by the expected content. For example:
To check an application that supports multiple hostnames, use relative URLs that include the hostname, for example:
You can also specify the protocol to explicitly check HTTPS requests.
The default behavior is to wait for 5 seconds before running the first check, and timeout each check to 30 seconds.
By default, checks will be attempted 5 times. (Retried 4 times)
You can change these by setting WAIT, TIMEOUT and ATTEMPTS to different values, for
example:
WAIT=30 # Wait 1/2 minute
TIMEOUT=60 # Timeout after a minute
ATTEMPTS=10 # attempt checks 10 times
/ My Amazing App
Example: Successful Rails Deployment
In this example, a rails applicaiton is successfully deployed to dokku. The initial round of checks fails while the server is starting, but once it starts they succeed and the deployment is successful. ATTEMPTS is set to 6, but the third attempt succeeds.
CHECKS file
Info
check.txt is a text file returning the string 'simple_check'
Deploy Output
Note
The output has been trimmed for brevity
git push dokku master
-----> Cleaning up...
-----> Building myapp from herokuish...
-----> Adding BUILD_ENV to build environment...
-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.0.0
.....
-----> Discovering process types
Procfile declares types -> web
-----> Releasing myapp...
-----> Deploying myapp...
-----> Running pre-flight checks
-----> Attempt 1/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/check.txt => "simple_check"
!
curl: (7) Failed to connect to 172.17.0.155 port 5000: Connection refused
! Check attempt 1/6 failed.
-----> Attempt 2/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/check.txt => "simple_check"
!
curl: (7) Failed to connect to 172.17.0.155 port 5000: Connection refused
! Check attempt 2/6 failed.
-----> Attempt 3/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/check.txt => "simple_check"
-----> All checks successful!
=====> myapp container output:
=> Booting Thin
=> Rails 4.2.0 application starting in production on http://0.0.0.0:5000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Thin web server (v1.6.3 codename Protein Powder)
Maximum connections set to 1024
Listening on 0.0.0.0:5000, CTRL+C to stop
=====> end myapp container output
-----> Running post-deploy
-----> Configuring myapp.dokku.example.com...
-----> Creating http nginx.conf
-----> Running nginx-pre-reload
Reloading nginx
-----> Shutting down old container in 60 seconds
=====> Application deployed:
http://myapp.dokku.example.com
Example: Failing Rails Deployment
In this example, a Rails application fails to deploy. The reason for the failure is that the postgres database connection fails. The initial checks will fail while we wait for the server to start up, just like in the above example. However, once the server does start accepting connections, we will see an error 500 due to the postgres database connection failure.
Once the attempts have been exceeded, the deployment fails and we see the container output, which shows the Postgres connection errors.
CHECKS file
Info
The check to the root url '/' would normally access the database.
Deploy Output
Note
The output has been trimmed for brevity
git push dokku master
-----> Cleaning up...
-----> Building myapp from herokuish...
-----> Adding BUILD_ENV to build environment...
-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.0.0
.....
Discovering process types
Procfile declares types -> web
Releasing myapp...
Deploying myapp...
Running pre-flight checks
-----> Attempt 1/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/ => ""
!
curl: (7) Failed to connect to 172.17.0.188 port 5000: Connection refused
! Check attempt 1/6 failed.
-----> Attempt 2/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/ => ""
!
curl: (7) Failed to connect to 172.17.0.188 port 5000: Connection refused
! Check attempt 2/6 failed.
-----> Attempt 3/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/ => ""
!
curl: (22) The requested URL returned error: 500 Internal Server Error
! Check attempt 3/6 failed.
-----> Attempt 4/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/ => ""
!
curl: (22) The requested URL returned error: 500 Internal Server Error
! Check attempt 4/6 failed.
-----> Attempt 5/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/ => ""
!
curl: (22) The requested URL returned error: 500 Internal Server Error
! Check attempt 5/6 failed.
-----> Attempt 6/6 Waiting for 5 seconds ...
CHECKS expected result:
http://localhost/ => ""
!
curl: (22) The requested URL returned error: 500 Internal Server Error
Could not start due to 1 failed checks.
! Check attempt 6/6 failed.
=====> myapp container output:
=> Booting Thin
=> Rails 4.2.0 application starting in production on http://0.0.0.0:5000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Thin web server (v1.6.3 codename Protein Powder)
Maximum connections set to 1024
Listening on 0.0.0.0:5000, CTRL+C to stop
Started GET "/" for 172.17.42.1 at 2015-03-26 21:36:47 +0000
Is the server running on host "172.17.42.1" and accepting
TCP/IP connections on port 5431?
PG::ConnectionBad (could not connect to server: Connection refused
Is the server running on host "172.17.42.1" and accepting
TCP/IP connections on port 5431?
):
vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `initialize'
vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `new'
vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `connect'
vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:242:in `initialize'
vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `new'
vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `postgresql_connection
=====> end myapp container output
/usr/local/bin/dokku: line 49: 23409 Killed dokku deploy "$APP"
To dokku@dokku.example.com:myapp
! [remote rejected] dokku -> master (pre-receive hook declined)
error: failed to push some refs to 'dokku@dokku.example.com:myapp'