Unable to query docker version: Get https://<ip>/v1.15/version: remote error: tls: bad certificate

GitLab CI/CD
1

After I re-installed gitlab runner I started to get the following errors:

tls_cert_error
tls_cert_error900×268 20.3 KB

I have the following config for my runner:

concurrent = 10
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "Builds coordinator"
  url = "https://gitlab.com/"
  token = "<token>"
  executor = "docker+machine"
  limit = 10
  [runners.docker]
    tls_verify = false
    image = "alpine:latest"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0
  [runners.machine]
    IdleCount = 0
    IdleTime = 0
    OffPeakTimezone = ""
    OffPeakIdleCount = 0
    OffPeakIdleTime = 0
    MachineDriver = "digitalocean"
    MachineName = "gitlab-runner-autoscale-%s"
    MachineOptions = [
        "digitalocean-image=coreos-stable",
        "digitalocean-ssh-user=core",
        "digitalocean-access-token=<token>",
        "digitalocean-region=lon1",
        "digitalocean-size=4gb",
        "digitalocean-private-networking"
    ]
  [runners.cache]
    Type = "s3"
    Path = "cache_for_builds"
    Shared = false
    [runners.cache.s3]
      ServerAddress = "ams3.digitaloceanspaces.com"
      AccessKey = "<key>"
      SecretKey = "<secret>"
      BucketName = "cache-for-builds"
      BucketLocation = "ams3"
      Insecure = false

I tried to do docker-machine ls when the build was running and I saw the following output:

... ERRORS
... Unknown   Unable to query docker version: Cannot connect to the docker engine endpoint

or

... ERRORS
... Unable to query docker version: Get https://<ip>:2376/v1.15/version: remote error: tls: bad certificate

I tried to search for certs on my server with find -name "*cert*" and found them in /root/.docker/machine/certs. I added path to the certs to the [runners.docker] section as described in the docs but it didn’t help:

[runners.docker]
  ...
  tls_cert_path = "/root/.docker/machine/certs"

When I view gitlab runner logs with journalctl -u gitlab-runner I see

Jan 13 21:06:59 builds-coordinator gitlab-runner[3360]: ERROR: Error creating machine: Error checking the host: Error checking and/or regenerating the certs: There was an error validating certificates for host "<ip>:2376": remote error: tls: bad certificate  driver=digitalocean name=r
Jan 13 21:06:59 builds-coordinator gitlab-runner[3360]: ERROR: You can attempt to regenerate them using 'docker-machine regenerate-certs [name]'.  driver=digitalocean name=runner-gitlab-runner-autoscale-<id> operation=create
Jan 13 21:06:59 builds-coordinator gitlab-runner[3360]: ERROR: Be advised that this will trigger a Docker daemon restart which might stop running containers.  driver=digitalocean name=runner-gitlab-runner-autoscale-<id> operation=create
Jan 13 21:06:59 builds-coordinator gitlab-runner[3360]: The default lines below are for a sh/bash shell, you can specify the shell you're using, with the --shell flag.  driver=digitalocean name=runner-gitlab-runner-autoscale-<id> operation=create
Jan 13 21:07:00 builds-coordinator gitlab-runner[3360]: WARNING: Machine creation failed, trying to provision  error=exit status 1 name=runner-gitlab-runner-autoscale-<id>
Jan 13 21:07:01 builds-coordinator gitlab-runner[3360]: Waiting for SSH to be available...                  name=runner-gitlab-runner-autoscale-<id> operation=provision

Before I was using gitlab runner version 11.5.1

docker info gives me

Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 0
Server Version: 18.06.1-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
runc version: 69663f0bd4b60df09991c08812a60108003fa340
init version: fec3683
Security Options:
 apparmor
 seccomp
  Profile: default
Kernel Version: 4.15.0-36-generic
Operating System: Ubuntu 18.04.1 LTS
OSType: linux
Architecture: x86_64
CPUs: 1
Total Memory: 1.947GiB
Name: builds-coordinator
ID: <ID>
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

Currently I am using gitlab runner 11.6.0:

Version:      11.6.0
Git revision: f100a208
Git branch:   11-6-stable
GO version:   go1.8.7
Built:        2018-12-22T11:56:10+0000
OS/Arch:      linux/amd64

How can I fix these errors and make gitlab runner running the builds?