DbHealthCheck.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Diagnostics.HealthChecks;
using System.Threading;
using System.Threading.Tasks;

public class DatabaseHealthCheck : IHealthCheck
{
    private readonly DbContext dbContext;

    public DatabaseHealthCheck(DbContext context)
    {
        this.dbContext = context;
    }

    public async Task<HealthCheckResult> CheckHealthAsync(
        HealthCheckContext context,
        CancellationToken cancellationToken = default(CancellationToken))
    {
        var canConnectToDatabase = 
            await dbContext.Database.CanConnectAsync();

        if (canConnectToDatabase)
            return HealthCheckResult.Healthy();

        return HealthCheckResult.Unhealthy();
    }
}