PortPatrol

PortPatrol is a simple Go application that checks if a specified TCP, HTTP or ICMP target is available. It continuously attempts to connect to the specified target at regular intervals until the target becomes available or the program is terminated. Intended to run as a Kubernetes initContainer, PortPatrol helps verify whether a dependency is ready. The configuration is done through startup arguments. You can check multiple targets at once.

Command-Line Flags

PortPatrol accepts the following command-line flags:

Common Flags

Flag	Type	Default	Description
--default-interval	duration	2s	Default interval between checks. Can be overridden for each target.
--version	bool	false	Show version and exit.
--help, -h	bool	false	Show help.

Target Flags

PortPatrol accepts "dynamic" flags that can be defined in the startup arguments. Use the --<TYPE>.<IDENTIFIER>.<PROPERTY>=<VALUE> format to define targets. Types are: http, icmp or tcp.

HTTP-Flags

• --http.<IDENTIFIER>.name = string The name of the target. If not specified, it uses the <IDENTIFIER> as the name.

• --http.<IDENTIFIER>.address = string The target's address. Resolvable: See Resolving Variables below.

  • --http.<IDENTIFIER>.interval = duration The interval between HTTP requests (e.g., 1s). Overwrites the global --default-interval.

• --http.<IDENTIFIER>.method = string The HTTP method to use (e.g., GET, POST). Defaults to GET.

• --http.<IDENTIFIER>.header = string A HTTP header in key=value format. Can be specified multiple times. Example: Authorization=Bearer token Resolvable: See Resolving Variables below.

• --http.<IDENTIFIER>.allow-duplicate-headers = bool Allow duplicate headers. Defaults to false.

• --http.<IDENTIFIER>.expected-status-codes = string A comma-separated list of expected HTTP status codes or ranges (e.g., 200,301-302). Defaults to 200.

• --http.<IDENTIFIER>.skip-tls-verify = bool Whether to skip TLS verification. Defaults to false.

• --http.<IDENTIFIER>.timeout = duration The timeout for the HTTP request (e.g., 5s). Defaults to 1s.

ICMP Flags

• --icmp.<IDENTIFIER>.name = string The name of the target. If not specified, it uses the <IDENTIFIER> as the name.

• --icmp.<IDENTIFIER>.address = string The target's address. Resolvable: See Resolving Variables below.

• --icmp.<IDENTIFIER>.interval = duration The interval between ICMP requests (e.g., 1s). Overwrites the global --default-interval.

• --icmp.<IDENTIFIER>.read-timeout = duration The read timeout for the ICMP connection (e.g., 1s). Defaults to 1s.

• --icmp.<IDENTIFIER>.write-timeout = duration The write timeout for the ICMP connection (e.g., 1s).Defaults to 1s.

TCP Flags

• --tcp.<IDENTIFIER>.name = string The name of the target. If not specified, it uses the <IDENTIFIER> as the name.

• --tcp.<IDENTIFIER>.address = string The target's address. Resolvable: See Resolving Variables below.

• --tcp.<IDENTIFIER>.interval = duration The interval between ICMP requests (e.g., 1s). Overwrites the global --default-interval.

Resolving variables

Each address field can be resolved using environment variables, files, JSON, YAML, and INI files.

• env: – Resolves environment variables. Example: env:PATH returns the value of the PATH environment variable.
• file: – Resolves values from a simple key-value file. Example: file:/config/app.txt//KeyName returns the value associated with KeyName in app.txt.
• json: – Resolves values from a JSON file. Supports dot notation for nested keys. Example: json:/config/app.json//database.host returns host field under database in app.json. It is also possible to indexing into arrays (e.g., json:/config/app.json//servers.0.host).
• yaml: – Resolves values from a YAML file. Supports dot notation for nested keys. Example: yaml:/config/app.yaml//server.port returns port under server in app.yaml.It is also possible to indexing into arrays (e.g., yaml:/config/app.yaml//servers.0.host).
• ini: – Resolves values from an INI file. Can specify a section and key, or just a key in the default section. Example: ini:/config/app.ini//Section.Key returns the value of Key under Section.
• No prefix – Returns the value as-is, unchanged.

HTTP headers values can also be resolved using the same mechanism, (from a environment variable --http.<IDENTIFIER>.header="header=env:SECRET_HEADER" or from a file --http.<IDENTIFIER>.header="header=file:PATH_TO_FILE").

Examples

Define an HTTP Target

portpatrol \
  --http.web.address=http://example.com:80 \
  --http.web.method=GET \
  --http.web.expected-status-codes=200,204 \
  --http.web.header="Authorization=Bearer token" \
  --http.web.header="Content-Type=application/json" \
  --http.web.skip-tls-verify=false \
  --default-interval=5s

Define Multiple Targets (HTTP and TCP) Running in Parallel

portpatrol \
  --http.web.address=http://example.com:80 \
  --tcp.db.address=tcp://localhost:5432 \
  --default-interval=10s

Notes

Proxy Settings: Proxy configurations (HTTP_PROXY, HTTPS_PROXY, NO_PROXY) are managed via environment variables.

Behavior Flowchart

TCP Check

Click here to see the flowchart

graph TD;
    classDef noFill fill:none;
    classDef violet stroke:#9775fa;
    classDef green stroke:#2f9e44;
    classDef error stroke:#fa5252;
    classDef transparent stroke:none,font-size:20px;

    subgraph MainFlow[ ]
        direction TB
        start((Start)) --> attemptConnect[Attempt to connect to <font color=orange>TARGET_ADDRESS</font>];
        class start violet;

        subgraph RetryLoop[Retry Loop]
            subgraph InnerLoop[ ]
                direction TB
                attemptConnect -->|Connection successful| targetReady[Target is ready];
                attemptConnect -->|Connection failed| waitRetry[Wait for retry <font color=orange>CHECK_INTERVAL</font>];
                waitRetry --> attemptConnect;
            end
        end

        targetReady --> processEnd((End));
        class processEnd violet;
        waitRetry --> processEnd;
    end

    programTerminated[Program terminated or canceled] --> processEnd;
    class programTerminated error;

    class start,attemptConnect,targetReady,waitRetry,processEnd,programTerminated,MainFlow,RetryLoop noFill;
    class MainFlow,RetryLoop transparent;

Loading

Permissions

Only when using ICMP checks in Kubernetes, it's important to ensure that the container has the necessary permissions to send ICMP packets. It is necessary to add the CAP_NET_RAW capability to the container's security context.

Example:

- name: wait-for-host
  image: ghcr.io/containeroo/portpatrol:latest
  env:
    - name: TARGET_ADDRESS
      value: icmp://hostname.domain.com
  securityContext:
    readOnlyRootFilesystem: true
    allowPrivilegeEscalation: false
    capabilities:
      add: ["CAP_NET_RAW"]

For TCP and HTTP checks, the container does not require any additional permissions.

HTTP Check

Click here to see the flowchart

flowchart TD;
    direction TB
    classDef noFill fill:none;
    classDef violet stroke:#9775fa;
    classDef green stroke:#2f9e44;
    classDef error stroke:#fa5252;
    classDef decision stroke:#1971c2;
    classDef transparent stroke:none,font-size:20px;

    subgraph MainFlow[ ]
        direction TB
        processStart((Start)) --> createRequest[Create HTTP request for <font color=orange>TARGET_ADDRESS</font>];
        class start processStart;

        createRequest --> addHeaders[Add headers from <font color=orange>HTTP_HEADERS</font>];
        addHeaders --> addSkipTLS[Add skip TLS verify if <font color=orange>HTTP_SKIP_TLS_VERIFY</font> is set];
        addSkipTLS --> sendRequest[Send HTTP request];

        subgraph RetryLoop[Retry Loop]
            subgraph InnerLoop[ ]
                direction TB
                sendRequest --> checkTimeout{Answers within <font color=orange>DIAL_TIMEOUT</font>?};
                class checkTimeout decision;
                checkTimeout -->|Yes| checkStatusCode[Check response status code <font color=orange>HTTP_EXPECTED_STATUS_CODES</font>];
                checkStatusCode --> statusMatch{Matches?};
                class statusMatch decision;

                statusMatch -->|Yes| targetReady[Target is ready];
                class targetReady success;

                statusMatch -->|No| targetNotReady[Target is not ready];
                class targetNotReady error;
                targetNotReady --> waitRetry[Wait for retry <font color=orange>CHECK_INTERVAL</font>];
                waitRetry --> sendRequest;
            end
        end

    targetReady --> processEnd((End));
    class processEnd violet;
    end

    programTerminated[Program terminated or canceled] --> processEnd;
    class programTerminated error;

class processStart,createRequest,addHeaders,addSkipTLS,sendRequest,checkTimeout,checkStatusCode,statusMatch,targetReady,targetNotReady,waitRetry,programTerminated,processEnd,MainFlow,RetryLoop noFill;
class MainFlow,RetryLoop transparent;

Loading

ICMP Check

Click here to see the flowchart

flowchart TD;
    direction TB
    classDef noFill fill:none;
    classDef violet stroke:#9775fa;
    classDef green stroke:#2f9e44;
    classDef error stroke:#fa5252;
    classDef decision stroke:#1971c2;
    classDef transparent stroke:none,font-size:20px;

    subgraph MainFlow[ ]
        direction TB
        processStart((Start)) --> createRequest[Create ICMP request for <font color=orange>TARGET_ADDRESS</font>];
        class start processStart;

        createRequest --> sendRequest[Send ICMP request];

        subgraph RetryLoop[Retry Loop]
            subgraph InnerLoop[ ]
                direction TB
                sendRequest --> checkTimeout{Answers within timeouts <font color=orange>DIAL_TIMEOUT</font>/<font color=orange>ICMP_READ_TIMEOUT</font>?};

                checkTimeout -->|Connection successful| targetReady[Target is ready];
                checkTimeout -->|Connection failed| waitRetry[Wait for retry <font color=orange>CHECK_INTERVAL</font>];
                waitRetry --> sendRequest;

            end
        end

    targetReady --> processEnd((End));
    class processEnd violet;
    end

    programTerminated[Program terminated or canceled] --> processEnd;
    class programTerminated error;

class processStart,createRequest,sendRequest,checkTimeout,targetReady,waitRetry,processEnd,MainFlow,RetryLoop noFill;
class MainFlow,RetryLoop transparent;

Loading

Kubernetes initContainer Configuration

Configure your Kubernetes deployment to use this init container:

initContainers:
  - name: wait-for-vm
    image: ghcr.io/containeroo/portpatrol:latest
    args:
      - --icmp.vm.address=hostname.domain.tld
    securityContext: # icmp requires CAP_NET_RAW
      readOnlyRootFilesystem: true
      allowPrivilegeEscalation: false
      capabilities:
        add: ["CAP_NET_RAW"]
  - name: wait-for-it
    image: ghcr.io/containeroo/portpatrol:latest
    args:
      - --target.postgres.address=postgres.default.svc.cluster.local:9000/healthz # use healthz endpoint to check if postgres is ready
      - --target.postgres.method=POST
      - --target.postgres.header=Authorization=env:BEARER_TOKEN
      - --target.postgres.expected-status-codes=200,202
      - --target.redis.name=redis
      - --target.redis.address=redis.default.svc.cluster.local:6437
      - --tcp.vaultkey.address=valkey.default.svc.cluster.local:6379
      - --tcp.vaultkey.interval=5s
      - --tcp.vaultkey.timeout=5s
    envFrom:
      - secretRef:
          name: bearer-token