This article shows an example of implementing a Readiness probe based on HTTP requests.
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This article does not include recommendations on how to define whether you need a Readiness probe.
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Basic information about the case
This is a module that includes two portable services. Service #1 can send information about its state via HTTP requests. Service #2 can interpret its responses or absence of responses.
We need to configure Service #2 so that it doesn’t accept incoming traffic when Service #1 is in a certain state.
We have decided to do it using a Readiness probe.
Modification of Service #2
We need to define how Service #2 processes the HTTP request that retrieves the status of Service #1.
From the SERV1URL environment variable, the address of Service #1 is retrieved. An HTTP request is sent to this service. If the response status code is 200, and the response body meets the conditions of the probe set up in Service #2, the method we added returns status 200. Otherwise, it returns 504.
func readnessFunc(w http.ResponseWriter, r *http.Request) {
if serv1URL, exists := os.LookupEnv("SERV1URL"); exists {
response, err := http.Get(serv1URL + "/getstatus")
if err == nil &&
response.StatusCode == 200 &&
isValidStatus(response.Body) {
fmt.Fprintf(w, "Yeah, it works")
return
}
}
w.WriteHeader(http.StatusGatewayTimeout)
}
Configure Service #2
When the image of Service #2 is built and uploaded, we need to configure the Readiness probe in BRIX. To do that, we need to:
- In the module’s settings, open the Services tab, then move on to editing Service #2.
- On the Readiness tab, select HTTP.
- Set a delay after which the probe is performed.
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Don’t make the delay too short. Service #2 must have enough time to be initialized in the cluster to accept requests from probes. If the value of the delay is not enough, Service #2 may become unavailable.
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- In Service #2, specify the port and the path to the HTTP method used for the probe.
- Pass information about the location of Service #1 to Service #2. To do that, go to the Environment Variables tab and create a string named SERV1URL with the URL of Service #1.
- Specify the address of the service by clicking the {+} symbol on the right side of the string and select the service from the list. A value of the following format will be generated:
{$_srv_ServiceName#1}.
Additional information
When developing and implementing a Readiness probe, note that it is performed all the time while Service #2 exists. In the example provided in this article, Service #2 will constantly send HTTP requests to Service #1.