Newer
Older
OpenAppStack Design
===================
This article covers the basic design of OpenAppStack.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
## Application build pipeline
The following diagram explains the process to go from an application's source
code to a deployment on OpenAppStack.
These are the steps in more detail:
- Build container (this process should be maintained by application developer by
providing a Dockerfile with the application)
1. Get application package (source code, installation package, etc.)
1. If not part of the package: get default configuration for the
application
1. Build container with application package installed
1. Install application dependencies
1. Install application package
1. Setup default configuration
1. Setup pluggable configuration override, can be:
- Reading environment variables
- Extra configuration file mounted into the container elsewhere
- Helm chart
- Deployment configuration to specify:
- The container(s) that should be deployed.
- The port(s) that they expose.
- Volume mounts for configuration files and secrets.
- Live/readyness probes
- Persistent storage locations and methods
- A lot of other things
- Service configuration to specify:
- Ports exposed to the user of the application
- Ingress configuration to specify:
- How to proxy to the application (which hostname or URL)
- Some authentication plugins (http auth, for example)
- Custom files:
- Add file templates for mountable application configuration files
- Files that specify integrations with other services
- Deploy
1. Create `values.yaml` file with the variables for the Helm deployment to
the Kubernetes cluster
1. "Manually" add secrets to the Kubernetes cluster.
1. Run `helm install` to install the customised application.
## Configuration
As can be seen in the images, applications are expected to have two different
types of configuration. Containers should provide a default configuration,
that at least configures things like the port the application runs on, the
locations for log files, etc.
What we call the *external configuration* is provided by the user. This includes
overrides of the default application, as well as variables like the hostname
that the application will run on and listen to and the title of the web
interface.
OpenAppStack will use Helm charts to provide the external configuration for the
"Deploy" step. Helm charts can contain configuration file templates with
default values that can be overridden during the installation or upgrade of a
helm chart.
## Application containers
For inclusion in OpenAppStack, it is required that the application developers
provide Docker containers for their applications. There are several reasons for
this:
- If application developers do not provide a container, chances are they also do
not think about how their application would update itself after a new
container is deployed. This can lead to problems with things like database
migrations.
- Maintaining the containerisation for an application can, in most cases, not be
fully automated.
### Container updates
When an application update is available, these updates need to be rolled out to
OpenAppStack instances. This will be done according the following steps:
1. Application container is built with new application source and tagged for
testing.
4. Helm chart for application is updated to provide new container.
3. Helm chart is deployed to an OpenAppStack test cluster following the steps in
the diagram above.
2. Application is tested with automated tests
3. If tests succeed, new container is tagged for release.
4. OpenAppStack automated update job fetches new Helm chart and upgrades current
instance using Helm.
Most of these steps can be developed by configuring a CI system and configuring
Kubernetes and Helm correctly. The automated update job that will run on
OpenAppStack clusters will be developed by us.
## Persistent data
Containerised applications are normally "stateless" (meaning no data is saved
inside the containers). However, it is possible to mount persistent volumes to
specific directories in the container, basically adding a persistent layer on
top of the containerised application. To provide this in OAS's simple setup, we
have developed a [local storage
provisioner](https://open.greenhost.net/openappstack/local-storage) that
automatically provides persistent data on the VPS running OAS to an application
that requests it.