How to use curl in Azure Functions and AWS Lambda

To use curl in Azure Functions or AWS Lambda with C#, add the CurlDotNet package to the function project and call Curl.ExecuteAsync (or CurlRequestBuilder) from your handler. It is a managed library, so there is no curl binary to bundle or install and nothing to start with Process.Start.

dotnet add package CurlDotNet

Azure Functions (isolated worker)

using CurlDotNet;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;

public class ProxyStatus
{
    [Function("ProxyStatus")]
    public async Task<HttpResponseData> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequestData req)
    {
        var result = await Curl.ExecuteAsync("curl -m 10 https://httpbin.org/json");
        var response = req.CreateResponse((System.Net.HttpStatusCode)result.StatusCode);
        await response.WriteStringAsync(result.Body ?? ""); return response;
    }
}

A timer-triggered health check is a common use: paste the curl command your on-call runbook already uses.

AWS Lambda

using Amazon.Lambda.Core;
using CurlDotNet.Core;

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

public class Function
{
    public async Task<int> Handler(string url, ILambdaContext context)
    {
        var result = await CurlRequestBuilder.Get(url)
            .WithTimeout(TimeSpan.FromSeconds(10)).ExecuteAsync();
        context.Logger.LogLine($"{url} -> {result.StatusCode}");
        return result.StatusCode;
    }
}

Calling AWS APIs with SigV4

--aws-sigv4 signs the request like the curl CLI does, which is handy for API Gateway endpoints with IAM auth:

using CurlDotNet;

var key = Environment.GetEnvironmentVariable("AWS_ACCESS_KEY_ID");
var secret = Environment.GetEnvironmentVariable("AWS_SECRET_ACCESS_KEY");

var result = await Curl.ExecuteAsync(
    $"curl --aws-sigv4 'aws:amz:us-east-1:execute-api' -u '{key}:{secret}' " +
    "https://abc123.execute-api.us-east-1.amazonaws.com/prod/items");

Inside Lambda, the role’s credentials also include a session token (AWS_SESSION_TOKEN) that AWS expects in the x-amz-security-token header. CurlDotNet signs every request header, so add it with -H "x-amz-security-token: $AWS_SESSION_TOKEN". The SigV4 examples on this page have not been run against a live AWS endpoint, so test against yours.

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