allow templating the ceos startup-config

docs/manual/kinds/ceos.md

@@ -109,7 +109,7 @@ cEOS nodes have a dedicated [`config`](../conf-artifacts.md#identifying-a-lab-di
 used as a startup config instead.
 
 #### Default node configuration
-When a node is defined without `config` statement present, containerlab will generate an empty config from [this template](https://github.com/srl-labs/containerlab/blob/master/nodes/crpd/crpd.cfg) and copy it to the config directory of the node.
+When a node is defined without `config` statement present, containerlab will generate an empty config from [this template](https://github.com/srl-labs/containerlab/blob/master/nodes/ceos/ceos.cfg) and copy it to the config directory of the node.
 
 ```yaml
 # example of a topo file that does not define a custom config
@@ -142,6 +142,31 @@ When a config file is passed via `config` parameter, it will override any config
 
 With such topology file containerlab is instructed to take a file `myconfig.conf` from the current working directory, copy it to the lab directory for that specific node under the `/flash/startup-config` name and mount that dir to the container. This will result in this config to act as a startup config for the node.
 
+It is possible to change the default config which every ceos node will start with with the following steps:
+
+1. Save the [default configuration template](https://github.com/srl-labs/containerlab/blob/master/nodes/ceos/ceos.cfg) under some local file name[^2] and add the necessary changes to it
+2. Use this file as a startup-config for ceos kind:
+    ```
+    name: ceos
+
+    topology:
+    kinds:
+        ceos:
+        startup-config: ceos-custom-startup.cfg
+    nodes:
+        # ceos1 will boot with ceos-custom-startup.cfg as set in the kind parameters
+        ceos1:
+        kind: ceos
+        image: ceos:4.25.0F
+        # ceos2 will boot with its own specific startup config, as it overrides the kind variables
+        ceos2: 
+        kind: ceos
+        image: ceos:4.25.0F
+        startup-config: node-specific-startup.cfg
+    links:
+        - endpoints: ["ceos1:eth1", "ceos2:eth1"]
+    ```
+
 #### Configuration persistency
 
 It is important to understand how configuration persistency behaves when a single lab is going through rounds of `deploy->destroy` actions.
@@ -221,3 +246,4 @@ As of this writing (22-June, 2021), ceos-lab image requires a cgroups v1 environ
 Consult your distribution's documentation for details regarding configuring cgroups v1 in case you see similar startup issues as indicated in [#467](https://github.com/srl-labs/containerlab/issues/467). 
 
 [^1]: https://eos.arista.com/ceos-lab-topo/
+[^2]: do not remove the template variables from the `Management0` interface, otherwise the nodes will not apply the IP address from docker IPAM service.

nodes/ceos/ceos.go

@@ -5,6 +5,7 @@
 package ceos
 
 import (
+	"bytes"
 	"context"
 	_ "embed"
 	"fmt"
@@ -141,38 +142,47 @@ func createCEOSFiles(node *types.NodeConfig) error {
 	return nil
 }
 
-func ceosPostDeploy(ctx context.Context, r runtime.ContainerRuntime, nodeCfg *types.NodeConfig) error {
+func ceosPostDeploy(ctx context.Context, r runtime.ContainerRuntime, node *types.NodeConfig) error {
 	// post deploy actions are not needed if a user specified startup config was provided
-	if nodeCfg.StartupConfig != "" {
-		return nil
+	// and it doesn't have templation vars for ipv4 management address
+	if node.StartupConfig != "" {
+		c, err := os.ReadFile(node.StartupConfig)
+		if err != nil {
+			return err
+		}
+		if !bytes.Contains(c, []byte("{{ if .MgmtIPv4Address }}")) {
+			return nil
+		}
+
+		cfgTemplate = string(c)
 	}
 
 	// regenerate ceos config since it is now known which IP address docker assigned to this container
-	err := nodeCfg.GenerateConfig(nodeCfg.ResStartupConfig, cfgTemplate)
+	err := node.GenerateConfig(node.ResStartupConfig, cfgTemplate)
 	if err != nil {
 		return err
 	}
 
-	err = r.StopContainer(ctx, nodeCfg.ContainerID)
+	err = r.StopContainer(ctx, node.ContainerID)
 	if err != nil {
 		return err
 	}
 	// remove the netns symlink created during original start
 	// we will re-symlink it later
-	if err := utils.DeleteNetnsSymlink(nodeCfg.LongName); err != nil {
+	if err := utils.DeleteNetnsSymlink(node.LongName); err != nil {
 		return err
 	}
 
-	err = r.StartContainer(ctx, nodeCfg.ContainerID)
+	err = r.StartContainer(ctx, node.ContainerID)
 	if err != nil {
 		return err
 	}
-	nodeCfg.NSPath, err = r.GetNSPath(ctx, nodeCfg.ContainerID)
+	node.NSPath, err = r.GetNSPath(ctx, node.ContainerID)
 	if err != nil {
 		return err
 	}
 
-	return utils.LinkContainerNS(nodeCfg.NSPath, nodeCfg.LongName)
+	return utils.LinkContainerNS(node.NSPath, node.LongName)
 }
 
 func (s *ceos) GetImages() map[string]string {