How Does Reloader Work?#
Reloader watches for ConfigMap
and Secret
and detects if there are changes in data of these objects. After change detection Reloader performs rolling upgrade on relevant Pods via associated Deployment
, Daemonset
and Statefulset
.
How Does Change Detection Work?#
Reloader watches changes in configmaps
and secrets
data. As soon as it detects a change in these. It forwards these objects to an update handler which decides if and how to perform the rolling upgrade.
Requirements for Rolling Upgrade#
To perform rolling upgrade a deployment
, daemonset
or statefulset
must have
- support for rolling upgrade strategy
- specific annotation for
configmaps
orsecrets
The annotation value is comma separated list of configmaps
or secrets
. If a change is detected in data of these configmaps
or secrets
, Reloader will perform rolling upgrades on their associated deployments
, daemonsets
or statefulsets
.
Annotation for Configmap#
For a Deployment
called foo
have a ConfigMap
called foo
. Then add this annotation* to your Deployment
, where the default annotation can be changed with the --configmap-annotation
flag:
metadata:
annotations:
configmap.reloader.stakater.com/reload: "foo"
Annotation for Secret#
For a Deployment
called foo
have a Secret
called foo
. Then add this annotation to your Deployment
, where the default annotation can be changed with the --secret-annotation
flag:
metadata:
annotations:
secret.reloader.stakater.com/reload: "foo"
Above mentioned annotation are also work for Daemonsets
Statefulsets
and Rollouts
How Does Rolling Upgrade Work?#
When Reloader detects changes in configmap. It gets two objects of configmap. First object is an old configmap object which has a state before the latest change. Second object is new configmap object which contains latest changes. Reloader compares both objects and see whether any change in data occurred or not. If Reloader finds any change in new configmap object, only then, it moves forward with rolling upgrade.
After that, Reloader gets the list of all deployments
, daemonsets
and statefulset
and looks for above mentioned annotation for configmap. If the annotation value contains the configmap name, it then looks for an environment variable which can contain the configmap or secret data change hash.
Environment Variable for ConfigMap#
If configmap name is foo then
STAKATER_FOO_CONFIGMAP
Environment Variable for Secret#
If Secret name is foo then
STAKATER_FOO_SECRET
If the environment variable is found then it gets its value and compares it with new configmap hash value. If old value in environment variable is different from new hash value then Reloader updates the environment variable. If the environment variable does not exist then it creates a new environment variable with latest hash value from configmap and updates the relevant deployment
, daemonset
or statefulset
Note: Rolling upgrade also works in the same way for secrets.
Hash Value Computation#
Reloader uses SHA1 to compute hash value. SHA1 is used because it is efficient and less prone to collision.
Monitor All Namespaces#
By default Reloader deploys in default namespace and monitors changes in all namespaces. To monitor changes in a specific namespace deploy the Reloader in that namespace and set the watchGlobally
flag to false
in values file located under deployments/kubernetes/chart/reloader
and render manifest file using helm command:
helm --namespace {replace this with namespace name} template . > reloader.yaml
The output file can then be used to deploy Reloader in specific namespace.
Compatibility With Helm Install and Upgrade#
Reloader has no impact on helm deployment cycle. Reloader only injects an environment variable in deployment
, daemonset
or statefulset
. The environment variable contains the SHA1 value of configmap's or secret's data. So if a deployment is created using Helm and Reloader updates the deployment, then next time you upgrade the helm release, Reloader will do nothing except changing that environment variable value in deployment
, daemonset
or statefulset
.