Dapr Basics

What is Dapr?

Abbreivation for "Distributed Application Runtime"

Dapr is a runtime/framework for developing event-driven microservices and cloud-native applications

Dapr can be installed by following the relevant instructions from the documentation

Getting Started

When using Dapr it's recommended that you also have Docker installed

Dapr works by deploying sidecar containers that manage communication and service invocation between services

To initialize Dapr you can run the following command to download the required binaries and config as well as start some of the required Docker containers:

dapr init

Thereafter, you can view the running containers that Dapr has initialized with:

docker ps

CONTAINER ID   IMAGE               COMMAND                  CREATED          STATUS                    PORTS                              NAMES
365529eb2137   daprio/dapr         "./placement"            19 minutes ago   Up 19 minutes             0.0.0.0:6050->50005/tcp            dapr_placement
86802da99f48   redis               "docker-entrypoint.s…"   20 minutes ago   Up 20 minutes             0.0.0.0:6379->6379/tcp             dapr_redis
0affbb4ed6d0   openzipkin/zipkin   "start-zipkin"           20 minutes ago   Up 20 minutes (healthy)   9410/tcp, 0.0.0.0:9411->9411/tcp   dapr_zipkin

And you can verify if the components directory was created

ls ~/.dapr

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----         3/26/2021   5:47 PM                bin
d-----         3/16/2021   4:10 PM                components
-a----         3/16/2021   4:10 PM            187 config.yaml

Run a Component

To run an application/component on Dapr, you use the dapr run command

Running the default Dapr components without actually running any other application can be done with:

dapr run --app-id myapp --dapr-http-port 3500

Which will run a blank app which only makes use of the default dapr redis and zipkin components as is defined in the ~/.dapr/components directory we saw above

Based on the default redis state store component that's defined in the Dapr instance, we can access the state store on http://localhost:3500/v1.0/state/statestore

Using this we can POST some key-value pair data to the endpoint, and retrieve it with the key

So to add something to the state store we can make the following HTTP Request by sending a collection of data:

POST /v1.0/state/statestore HTTP/1.1
Host: localhost:3500
Content-Type: application/json
Content-Length: 65

[
    {
        "key": "init_post",
        "value": "Hello, World!"
    }
]

We can then retreive the data we sent with:

GET /v1.0/state/statestore/init_post HTTP/1.1
Host: localhost:3500

Which will respond with:

"Hello, World!"

We can also log into redis from Docker to view all data in the Redis instance with:

docker exec -it dapr_redis redis-cli

And then we can run the following command to view the data in Redis:

> keys *

1) "myapp||init_post"

To view the type of the value that Dapr saves the data as:

> type "myapp||init_post

hash

Since the type is hash we need to use hgetall to get the value

> hgetall "myapp||init_post"

1) "data"
2) "\"Hello, World!\""
3) "version"
4) "1"

Additionally, Dapr apps are managed using components which are defined using yml, there are a number of Quickstart guides on this here